Scratch-resistant aqueous 2K PU coatings

Abstract

The invention relates to aqueous two-component coating compositions based on preferably hydroxy-functional and/or amino-functional aqueous polymer dispersions and thioallophanates containing silane groups as crosslinking agents, to a method for producing them and to the use of these coating compositions for producing coatings.

Claims

1. An aqueous coating composition comprising A) at least one polyisocyanate component, B) at least one aqueous polymer dispersion, C) optionally at least one catalyst for the crosslinking of silane groups and D) optionally further auxiliaries and additives, where the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the general formula (I), ##STR00005## in which R.sup.1, R.sup.2 and R.sup.3 are identical or different radicals and are each a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or an optionally substituted aromatic or araliphatic radical having up to 18 carbon atoms, which may optionally contain up to 3 heteroatoms from the series of oxygen, sulphur and nitrogen, X is a linear or branched organic radical having at least 2 carbon atoms, Y is a linear or branched, aliphatic or cycloaliphatic, an ariphatic or aromatic radical having up to 18 carbon atoms and n is an integer from 1 to 20.

2. The coating composition according to claim 1, characterized in that the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the formula (I), in which R.sup.1, R.sup.2 and R.sup.3 are identical or different radicals and are each a saturated, linear or branched, aliphatic or cycloaliphatic radical having up to 6 carbon atoms, and optionally contain up to 3 oxygen atoms, and X is a linear or branched alkylene radical having 2 to 10 carbon atoms, and Y and n are as defined in claim 1.

3. The coating composition according to claim 1, characterized in that the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the formula (I), in which R.sup.1, R.sup.2 and R.sup.3 are each alkyl radicals having up to 6 carbon atoms and/or alkoxy radicals which contain up to 3 oxygen atoms, with the proviso that at least one of the radicals R.sup.1, R.sup.2 and R.sup.3 is such an alkoxy radical, and X is a propylene radical (CH.sub.2CH.sub.2CH.sub.2), Y and n are as defined in claim 1.

4. The coating composition according to claim 1, characterized in that the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the formula (I), in which R.sup.1, R.sup.2 and R.sup.3 are identical or different radicals and are each methyl, methoxy or ethoxy, with the proviso that at least one of the radicals R.sup.1, R.sup.2 and R.sup.3 is a methoxy or ethoxy radical, X is a propylene radical (CH.sub.2CH.sub.2CH.sub.2), and Y and n are as defined in claim 1.

5. The coating composition according to claim 1, characterized in that the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the formula (I), in which Y is a linear or branched, aliphatic or cycloaliphatic radical having 5 to 13 carbon atoms.

6. The coating composition according to claim 1, characterized in that the polyisocyanate component A) comprises at least one thioallophanate containing silane groups, of the formula (I), in which Y is an aliphatic and/or cycloaliphatic radical as obtained by removing the isocyanate groups from a diisocyanate selected from the series of 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 2,4- and/or 4,4-diisocyanatodicyclohexylmethane.

7. The coating composition according to claim 1, characterized in that the aqueous polymer dispersion B) comprises at least one aqueous or water-dispersible polyacrylate resin, polyester resin, polyurethane resin, polyurea resin, polycarbonate resin and/or polyether resin.

8. The coating composition according to claim 7, characterized in that the aqueous polymer dispersion B) comprises at least one aqueous secondary polyacrylate dispersion B.sub.1), a polyester-polyacrylate-dispersion B.sub.3) and/or a polyurethane dispersion B.sub.4) based on polyester polyols, polycarbonate polyols and/or C3 and C4 polyether polyols.

9. The coating composition according to claim 7, characterized in that the aqueous polymer dispersion B) contains hydroxyl groups and/or amino groups.

10. The coating composition according to claim 9, characterized in that the catalyst C) comprises at least one amine-blocked acidic phosphoric ester, an amine-blocked sulphonic acid and/or at least one tetraalkylammonium carboxylate.

11. The coating composition according to claim 9, characterized in that the catalyst component C) comprises at least one amine-blocked phosphoric acid phenyl ester, an amine-blocked phosphoric acid bis(2-ethylhexyl) ester, tetraethylammonium benzoate and/or tetrabutylammonium benzoate.

12. A method for producing the coating composition according to claim 1, comprising mixing components A), B), optionally C) and optionally D) in any order in succession or together in proportions such that for each hydroxyl and/or amino group of the polymer dispersion B) there are from 0.5 to 2.0 isocyanate groups of the polyisocyanate component A).

13. A method for producing polyurethane paints and coatings comprising curing the coating composition according to claim 1.

14. The method according to claim 13, characterized in that the coating compositions are cured in a temperature range from 20 to 200 C. during a time of 1 min to 24 h.

15. A substrates coated with the coating composition according to claim 1.

16. A method for producing the coating composition according to claim 1, comprising mixing components A), B), optionally C) and optionally D) in any order in succession or together in proportions such that for each hydroxyl and/or amino group of the polymer dispersion B) there are from 0.6 to 1.8 isocyanate groups of the polyisocyanate component A).

17. A method for producing the coating composition according to claim 1, comprising mixing components A), B), optionally C) and optionally D) in any order in succession or together in proportions such that for each hydroxyl and/or amino group of the polymer dispersion B) there are from 0.7 to 1.5 isocyanate groups of the polyisocyanate component A).

18. The method according to claim 13, characterized in that the coating compositions are cured in a temperature range from 30 to 190 C. during a time of 2 min to 12 h.

19. The method according to claim 13, characterized in that the coating compositions are cured in a temperature range from 50 to 180 C. during a time of 3 min to 8 h.

Description

EXAMPLES

(1) All percentages are based on weight, unless stated otherwise.

(2) The NCO contents were determined by titrimetric means to DIN EN ISO 11909:2007-05.

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

(4) All of the viscosity measurements took place with a PhysicAMCR 51 rheometer from Anton Paar Germany GmbH in accordance with DIN EN ISO 3219:1994-10 at a shearing rate of 250 1/s.

(5) The amounts (mol %) of the isocyanate follow-on productsthiourethane, thioallophanate and isocyanurateproduced during the preparation of the thioallophanates containing silane groups (starting compounds A)) were computed from the integrals of proton-decoupled 13C NMR spectra (recorded on a Bruker DPX-400 instrument), and they relate in each case to the sum of thiourethane, thioallophanate and isocyanurate groups present. The chemical shifts (in ppm) of the individual structural elements are as follows: thiourethane: 166.8; thioallophanate: 172.3 and 152.8; isocyanurate: 148.4.

(6) The gloss of the coatings obtained was measured using a BYK-Gardner micro-TRi-gloss reflectometer in accordance with DIN EN ISO 2813:1999-06 at angles of 20 and 60.

(7) The pendulum damping by the Knig method was determined in accordance with DIN EN ISO 1522:2007-04 on glass plates.

(8) The wet scratch resistance of the coatings was tested using an Amtec-Kistler laboratory wash unit in accordance with DIN EN ISO 20566:2010-08, with subsequent determination of the residual gloss at 20 and 60.

(9) The resistance towards dry scratching was determined using a CM-5 crockmeter (from Atlas Electric Devices Co.) in accordance with DIN EN ISO 105-X12:2002-12 with 10 double rubs and an applied force of 9 N, using 9 281Q sandpaper (from 3M Deutschland GmbH), with subsequent determination of the residual gloss at 20 and 60.

(10) The figures for the wet scratching and dry scratching are expressed as % of residual gloss, measured immediately after scratching and also after reflow conditions, i.e. two-hour storage at 60 C., relative in each case to the initial gloss of the coating.

(11) The accelerated weathering test was carried out according to DIN EN ISO 16474/2:2014-03 method A, cycle 1 (102:18) in a Ci5000 weathering ometer from (Atlas Material Testing Technology GmbH).

(12) Preparation of the Starting Materials:

(13) Polyisocyanate Component A1)

(14) 1008 g (6 mol) of hexamethylene diisocyanate (HDI) were introduced under dry nitrogen with stirring at a temperature of 80 C. and 196 g (1.0 mol) of mercaptopropyltrimethoxysilane were added over the course of 30 minutes. The reaction mixture was stirred further at 80 C. until, after about 6 hours, the NCO content of 38.4% was reached, corresponding to complete thiourethanization.

(15) At this juncture the reaction mixture was sampled and the composition of the sample was determined by .sup.13C-NMR spectroscopy. According to this analysis, thiourethane groups were present exclusively. The .sup.13C-NMR spectrum showed no signals of thioallophanate or isocyanurate groups.

(16) By addition of 0.1 g of zinc(II) 2-ethyl-1-hexanoate as catalyst to the reaction mixture, which was at 80 C., the thioallophanatization reaction was initiated, with the temperature rising up to 85 C. on the basis of the reaction with its exothermic onset. Stirring continued at 85 C. until, about an hour after addition of the catalyst, the NCO content had dropped to 34.9%. The reaction was stopped by addition of 0.1 g of orthophosphoric acid and the unreacted monomeric HDI was removed in a thin-film evaporator at a temperature of 130 C. and a pressure of 0.1 mbar. This gave 538 g of a virtually colourless, clear polyisocyanate mixture whose characteristics and composition were as follows:

(17) NCO content: 14.4%

(18) Monomeric HDI: 0.08%

(19) Viscosity (23 C.): 291 mPas

(20) Thiourethane: 0.0 mol %

(21) Thioallophanate: 91.2 mol %

(22) Isocyanurate groups: 8.8 mol %

(23) Pollisocyanate Component A2)

(24) 1008 g (6 mol) of hexamethylene diisocyanate (HDI) were introduced under dry nitrogen with stirring at a temperature of 80 C., and 0.1 g of zinc(II) 2-ethyl-1-hexanoate as catalyst was added. Over a period of about 30 minutes, 196 g (1.0 mol) of mercaptopropyltrimethoxysilane were added dropwise, the temperature of the mixture rising up to 85 C. on account of the reaction with its exothermic onset.

(25) The reaction mixture was stirred further at 85 C. until after about 2 hours the NCO content dropped to 34.9%. The catalyst was deactivated by addition of 0.1 g of orthophosporic acid and the unreacted monomeric HDI was removed in a thin-film evaporator at a temperature of 130 C. and a pressure of 0.1 mbar. This gave 523 g of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(26) NCO content: 14.2%

(27) Monomeric HDI: 0.05%

(28) Viscosity (23 C.): 249 mPas

(29) Thiourethane: 0.0 mol %

(30) Thioallophanate: 98.5 mol %

(31) Isocyanurate groups: 1.5 mol %

(32) Polyisocyanate Component A3)

(33) In accordance with the method described for polyisocyanate component B 2), 1344 g (8 mol) of HDI were reacted in the presence of 0.15 g of zinc(II) 2-ethyl-1-hexanoate with 196 g (1.0 mol) of mercaptopropyltrimethoxysilane at a temperature of 85 C. until the NCO content was 38.2%. After the reaction had been stopped with 0.15 g of orthophosphoric acid and the reaction mixture had been worked up by distillation in a thin-film evaporator, 528 g were obtained of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(34) NCO content: 15.2%

(35) Monomeric HDI: 0.12%

(36) Viscosity (23 C.): 209 mPas

(37) Thiourethane: 0.0 mol %

(38) Thioallophanate: 99.0 mol %

(39) Isocyanurate groups: 1.0 mol %

(40) Polyisocyanate Component A4)

(41) In accordance with the method described for polyisocyanate component B 2), 672 g (4 mol) of HDI were reacted in the presence of 0.1 g of zinc(II) 2-ethyl-1-hexanoate with 196 g (1.0 mol) of mercaptopropyltrimethoxysilane at a temperature of 85 C. until the NCO content was 29.0%. After the reaction had been stopped with 0.1 g of orthophosphoric acid and the reaction mixture had been worked up by distillation in a thin-film evaporator, 486 g were obtained of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(42) NCO content: 12.9%

(43) Monomeric HDI: 0.06%

(44) Viscosity (23 C.): 298 mPas

(45) Thiourethane: 0.0 mol %

(46) Thioallophanate: 98.3 mol %

(47) Isocyanurate groups: 1.7 mol %

(48) Polyisocyanate Component A5)

(49) In accordance with the method described for polyisocyanate component B 2), 756 g (4.5 mol) of HDI were reacted in the presence of 0.1 g of zinc(II) 2-ethyl-1-hexanoate with 294 g (1.5 mol) of mercaptopropyltrimethoxysilane at a temperature of 85 C. until the NCO content was 24.0%. After the reaction had been stopped with 0.1 g of orthophosphoric acid and the reaction mixture had been worked up by distillation in a thin-film evaporator, 693 g were obtained of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(50) NCO content: 11.8%

(51) Monomeric HDI: 0.06%

(52) Viscosity (23 C.): 452 mPas

(53) Thiourethane: 0.0 mol %

(54) Thioallophanate: 99.0 mol %

(55) Isocyanurate groups: 1.0 mol %

(56) Silane group content: 25.9% (calculated as Si(OCH.sub.3).sub.3; mol. weight=121 g/mol)

(57) Polyisocyanate Component A6)

(58) In accordance with the method described for polyisocyanate component B 2), 756 g (4.5 mol) of HDI were reacted in the presence of 0.1 g of zinc(II) 2-ethyl-1-hexanoate with 357 g (1.5 mol) of mercaptopropyltriethoxysilane at a temperature of 85 C. until the NCO content was 22.6%. After the reaction had been stopped with 0.1 g of orthophosphoric acid and the reaction mixture had been worked up by distillation in a thin-film evaporator, 715 g were obtained of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(59) NCO content: 11.3%

(60) Monomeric HDI: 0.21%

(61) Viscosity (23 C.): 267 mPas

(62) Thiourethane: 0.0 mol %

(63) Thioallophanate: 98.4 mol %

(64) Isocyanurate groups: 1.6 mol %

(65) Polyisocyanate Component A7)

(66) 504 g (3.0 mol) of HDI were introduced under dry nitrogen with stirring at a temperature of 80 C., and 588 g (3.0 mol) of mercaptopropyltrimethoxysilane were added over the course of 30 minutes. The reaction mixture was stirred further at 80 C. until after about 12 hours the NCO content of 11.5% was reached, corresponding to complete thiourethanization. 0.1 g of zinc(II) 2-ethyl-1-hexanoate was added as catalyst to the reaction mixture, which was at 80 C., whereupon the temperature rose up to 85 C. owing to the thioallophanatization reaction with its exothermic onset. The mixture was stirred further at 85 C. until after about 4 hours from addition of catalyst, the NCO content dropped to 3.0%. The reaction was subsequently stopped by addition of 0.1 g of orthophosphoric acid. This gave a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(67) NCO content: 3.0%

(68) Monomeric HDI: 0.69%

(69) Viscosity (23 C.): 9220 mPas

(70) Thiourethane: 23.2 mol %

(71) Thioallophanate: 66.6 mol %

(72) Isocyanurate groups: 10.2 mol %

(73) Polyisocyanate Component A8)

(74) 1332 g (6 mol) of isophorone diisocyanate (IPDI) were introduced under dry nitrogen with stirring at a temperature of 95 C., and 0.2 g of zinc(II) 2-ethyl-1-hexanoate as catalyst was added. Over a period of about 30 minutes, 196 g (1.0 mol) of mercaptopropyltrimethoxysilane were added dropwise, with the temperature of the mixture rising to 103 C. owing to the reaction with its exothermic onset. The reaction mixture was stirred further at 100 C. until after about 5 hours the NCO content dropped to 27.4%. The catalyst was deactivated by addition of 0.2 g of orthophosphoric acid, and the unreacted monomer IPDI was removed in a thin-film evaporator at a temperature of 160 C. and a pressure of 0.1 mbar. This gave 659 g of a pale yellow, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(75) NCO content: 11.6%

(76) Monomeric IPDI: 0.46%

(77) Viscosity (23 C.): 11 885 mPas

(78) Thiourethane: 1.3 mol %

(79) Thioallophanate: 93.4 mol %

(80) Isocyanurate groups: 4.3 mol %

(81) Polyisocyanate Component A9)

(82) 756 g (4.5 mol) of HDI at a temperature of 80 C., under dry nitrogen and with stirring, were admixed dropwise over a period of about 30 minutes with 196 g (1.0 mol) of mercaptopropyltrimethoxysilane. The reaction mixture was subsequently heated to 140 C. and stirred further until after about 5 hours the NCO content had dropped to 24.0%. Distillative work-up in a thin-film evaporator gave 685 g of a virtually colourless, clear polyisocyanate mixture, whose characteristics and composition were as follows:

(83) NCO content: 11.8%

(84) Monomeric HDI: 0.08%

(85) Viscosity (23 C.): 447 mPas

(86) Thiourethane: 0.0 mol %

(87) Thioallophanate: 98.6 mol %

(88) Isocyanurate groups: 1.4 mol %

(89) Polyisocyanate Components A10)-A13) and Comparative Polyisocyanate C1)

(90) 80 parts by weight of a low-monomer-content polyisocyanurate polyisocyanate based on HDI, with an NCO content of 21.6%, an average isocyanate functionality of 3.5 and a viscosity (23 C.) of 3200 mPas, were admixed with 20 parts by weight of the thioallophanate polyisocyanate A5) and homogenized by 30 minutes of stirring at 60 C. to give a silane-functional polyisocyanate mixture A10). By the same method, using the amounts listed in Table 1 below of the same starting components, the silane-functional polyisocyanate mixtures A11) to A13) were produced.

(91) For comparison, drawing on Example 1 of WO 2009/156148, solvent-free reaction of 79 parts by weight of the above-described low-monomer-content polyisocyanurate polyisocyanate based on HDI (NCO content: 21.6%; average NCO functionality: 3.5; viscosity (23 C.): 3200 mPas) with 21 parts by weight of mercaptopropyltrimethoxysilane in the presence of 500 ppm of dibutyltin dilaurate as catalyst at 60 C. produced a partly silanized HDI trimer (comparative polyisocyanate C1).

(92) Table 1 below shows compositions (parts by weight) and characteristics of the silane-functional polyisocyanate mixtures A10) to A13) and also the characteristics of comparative polyisocyanate C1) according to WO 2009/156148.

(93) TABLE-US-00001 TABLE 1 Polyisocyanate A10) A11) A12) A13) C1) HDI polyisocyanurate 80 70 60 50 Polyisocyanate A5) 20 30 40 50 NCO content [%] 19.6 18.7 17.6 16.7 12.6 Viscosity (23 C.) 2240 1820 1490 1210 11800 [mPas] average NCO 3.2 3.1 2.9 2.8 2.6 functionality

(94) A direct comparison of the silane-functional polyisocyanate mixture A13) with the comparative polyisocyanate C1) according to WO 2009/156148, both having a silane group content (calculated as Si(OCH.sub.3).sub.3; mol. weight=121 g/mol) of 13%, impressively demonstrates the distinct advantage of the silane-functional thioallophanate polyisocyanates in terms of isocyanate content, isocyanate functionality and viscosity relative to the existing state of the art.

(95) Comparative Polyisocyanate C2) (Silane Group-free)

(96) HDI polyisocyanate containing isocyanurate and iminooxadiazinedione groups, prepared in accordance with Example 4 of EP-A 0 962 455, by trimerization of HDI using a 50% solution of tetrabutylphosphonium hydrogendifluoride in isopropanol/methanol (2:1) as catalyst. The reaction was stopped when the NCO content of the crude mixture was 43%, by addition of dibutyl phosphate. Subsequently, unconverted HDI was removed by thin-film distillation at a temperature of 130 C. and a pressure of 0.2 mbar.

(97) NCO content: 23.4%

(98) NCO functionality: 3.2

(99) Monomeric HDI: 0.2%

(100) Viscosity (23 C.): 700 mPas

(101) Isocyanurate: 49.9 mol %

(102) Iminooxadiazinedione 45.3 mol %

(103) Uretdione 4.8 mol %

Examples 1 and 2 (Inventive and Comparative)

(104) An inventive coating composition was produced by mixing 100 parts by weight of a commercial aqueous hydroxy-functional polyacrylate dispersion having a solids content of 42% and an OH content of 5.0%, based on resin solids, available under the name Bayhydrol A 2695 (Bayer MaterialScience AG, Leverkusen), with 0.21 part by weight of a commercial silicone surfactant (Byk-349, Byk Chemie GmbH), 0.49 part by weight of a 10% aqueous solution of a commercial silicone surface additive (Byk-378, Byk Chemie GmbH), 0.44 part by weight of a commercial fluorosurfactant (Novec FC-4430, 3M Deutschland GmbH) and 0.49 part by weight of a commercial thickener (Borchi Gel PW 25, OMG Borchers GmbH) and diluting the mixture with 14.0 parts by weight of water.

(105) Added to this batch were 93.2 parts by weight of a crosslinker solution consisting of 88.2 parts by weight of a 65% solution of the silane-group-containing thioallophanate A5) in MPA, 3.0 parts by weight of 50% solution of a commercial UV absorber (Tinuvin 348-2, BASF SE) in MPA and 2.0 parts by weight of a 50% solution of a commercial radical scavenger (Tinuvin 292, BASF SE) in MPA (corresponding to an equivalent ratio of isocyanate groups to alcoholic hydroxyl groups of 1.3:1), and the mixture was homogenized by stirring for 5 minutes at 1000 rpm.

(106) For comparison, the same method was used to formulate a paint batch from 100 parts by weight of Bayhydrol A 2695, using the additives specified above, and this batch was admixed with 47.5 parts by weight of a crosslinker solution, consisting of 44.5 parts by weight of a 65% solution of the comparative polyisocyanate C2) in MPA, 2.1 parts by weight of a 50% solution of a commercial UV absorber (Tinuvin 348-2, BASF SE) in MPA and 0.9 part by weight of a 50% solution of a commercial radical scavenger (Tinuvin 292, BASF SE) in MPA, (corresponding to an equivalent ratio of isocyanate groups to alcoholic hydroxyl groups of 1.3:1).

(107) The working life of the two application-ready coating compositions produced in this way was about 2 hours in each case.

(108) For determination of the pendulum damping, the two coating compositions were each applied to glass plates in an application film thickness of 60 m, using a four-way bar applicator, with drying in one instance at room temperature (about 20 C.) and, after 15 minutes of flashing in each case, under forced conditions (30 min/60 C.).

(109) The scratch resistance was tested on complete multi-coat paint systems. For this purpose, the inventive coating composition and the comparative coating composition were applied as clearcoats in an application film thickness of 60 m, using a four-way bar applicator, to aluminium panels which had been coated beforehand with a commercial 1 component OEM waterborne surfacer and with a conventional black 1-component OEM waterborne basecoat.

(110) Table 2 below shows the results of the performance tests in a comparison.

(111) TABLE-US-00002 TABLE 2 Example 1 2 (comparative) Drying conditions RT 2 h/60 C. RT 2 h/60 C. Pendulum damping after 1 day 38 s 93 s 133 s 184 s after 7 days 152 s 165 s 166 s 188 s after 14 days 180 s 183 s 172 s 194 s Initial gloss (20/60) 96/99 96/98 90/97 94/98 Wet scratching, relative immediate 63.3/63.4 61.8/77.7 33.3/59.8 37.9/63.4 residual gloss (20/60) after reflow 70.0/78.7 70.8/79.8 36.9/60.9 42.5/65.6 Dry scratching, relative immediate 26.7/70.2 29.2/70.2 26.2/67.4 21.8/63.4 residual gloss (20/60) after reflow 95.6/97.9 87.6/92.6 47.6/78.3 44.8/77.4 Accelerated weathering start 96/99 96/98 90/97 94/98 (20/60) after 500 h 98/100 98/100 72/92 92/97 after 1000 h 97/99 98/99 74/92 92/96 after 1500 h 97/99 98/100 80/94 93/97 after 2000 h 97/99 98/99 77/93 93/97 after 2500 h 93/96 93/96 75/90 88/94 E after 2500 h 0.5 0.6 0.8 0.9

(112) The comparison shows that the coating film obtained from the coating composition of the invention has a significantly higher residual gloss, immediately after wet scratching, than the coating material crosslinked with the standard polyisocyanate. With dry scratching, both coating films initially suffer a similarly severe loss of gloss, but under reflow conditions the coating material of the invention regains close to its original gloss. In the accelerated weathering test, furthermore, the coating material of the invention is notable for significantly better gloss retention and less yellowing.