RESISTANT 2K-PUR COATINGS

Abstract

The invention relates to coating agents containing A) at least one polyol component, B) at least one crosslinking component which is obtained by reacting at least one polyisocyanate with at least one amino functional alkoxy silane and which comprises free and/or blocked isocyanate groups, optionally (C) at least one catalyst for crosslinking silane groups, and D) optionally additional auxiliary agents and additives. The invention is characterized in that the polyol component A) comprises at least one polyester polyol A1) that has been produced using a 2,2,4,4-tetraalkylcyclobutane-1,3-diol (TACD) of the general formula (I), in which independently of one another the groups R.sup.1, R.sup.2, R.sup.3, and R.sup.4 represent linear or branched alkyl groups with up to 8 carbon atoms. The invention additionally relates to the use of the coating agents and to substrates which are coated with the coating agents according to the invention.

Claims

1: A coating composition containing A) at least one polyol component, B) at least one crosslinker component having free and/or blocked isocyanate groups obtained by reaction of at least one polyisocyanate with at least one amino-functional alkoxysilane, optionally C) at least one catalyst for the crosslinking of silane groups, and D) optionally further auxiliaries and additives, wherein the polyol component A) comprises at least one polyester polyol A1) prepared using a 2,2,4,4-tetraalkylcyclobutane-1,3-diol (TACD) of the general formula (I) ##STR00011## in which the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently linear or branched alkyl radicals having up to 8 carbon atoms.

2: The coating composition as claimed in claim 1, wherein the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4 in general formula (I) are independently linear or branched alkyl radicals having up to 6 carbon atoms.

3: The coating composition as claimed in claim 1, wherein the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.4 in general formula (I) are each a methyl radical.

4: The coating composition as claimed in claim 1, wherein preparation of the polyester polyol A1) involves including 2,2,4,4-tetraalkylcyclobutane-1,3-diols (TACDs) of general formula (I) in amounts that the TACD content in the total amount of polyhydric alcohols used is at least 10 mol %.

5: The coating composition as claimed in claim 1, wherein the polyester polyols A1) have a hydroxyl group content of 1.5% to 15% by weight, an acid number of 0 to 80 mg KOH/g and number-average molecular weights (Mn) of 300 to 10 000 g/mol.

6: The coating composition as claimed in claim 1, wherein the polyol component A) comprises further polyols A2) which are different from A1), selected from the group consisting of TACD-free polyester polyols, polyether polyols, polycarbonate polyols, polyacrylate polyols, and mixtures of those polyols, and wherein the content of polyester polyols A1) in the overall polyol component A) is at least 10% by weight.

7: The coating composition as claimed in claim 1, wherein preparation of crosslinker component B) includes isocyanurate group-containing polyisocyanates having aliphatically and/or cycloaliphatically bonded isocyanate groups, and/or isocyanurate group-containing and/or urethane group-containing polyisocyanates based on 2,4- and 2,6-diisocyanatotoluene.

8: The coating composition as claimed in claim 1, wherein preparation of crosslinker component B) includes polyisocyanates based on one selected from the group consisting of 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane and 4,4′-diisocyanatodicyclohexylmethane.

9: The coating composition as claimed in claim 1, wherein preparation of crosslinker component B) includes aminosilanes of the general formula (II) ##STR00012## wherein R.sup.5, R.sup.6 and R.sup.7 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 which has up to 18 carbon atoms and may optionally contain up to 3 heteroatoms selected from the group consisting of oxygen, sulfur and nitrogen, X is a linear or branched organic radical which has at least 2 carbon atoms and may optionally contain up to 2 imino groups (—NH—), and R.sup.8 is hydrogen, a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or an optionally substituted aromatic or araliphatic radical having up to 18 carbon atoms or a radical of the formula ##STR00013## in which R.sup.5, R.sup.6, R.sup.7 and X have the definition given above.

10: The coating composition as claimed in claim 1, wherein the aminosilanes included in preparation of crosslinker component B) are selected from the group consisting of N-methyl-3-aminopropyltrimethoxysilane, N-methyl-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxysilane, bis(3-trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)amine and mixtures of at least two of these.

11: The coating composition as claimed in claim 1, wherein preparation of crosslinker component B) includes aminosilanes of the general formula (III) ##STR00014## wherein R.sup.5, R.sup.6 and R.sup.7 have the definition given for formula (II) in claim 9, X is a linear or branched organic radical having at least 2 carbon atoms and R.sup.9 and R.sup.10 independently of one another are saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or aromatic organic radicals which have 1 to 18 carbon atoms, are substituted or unsubstituted and/or have heteroatoms in the chain.

12: The coating composition as claimed in claim 1, wherein preparation of crosslinker component B) includes aminosilanes of the general formula (V) ##STR00015## wherein R.sup.5, R.sup.6 and R.sup.7 have the definition given for formula (II) in claim 9, X is a linear or branched organic radical having at least 2 carbon atoms and R.sup.11 is a saturated linear or branched, aliphatic or cycloaliphatic organic radical having 1 to 8 carbon atoms.

13: The coating composition as claimed in claim 1, wherein catalysts C) are selected from the group consisting of phosphoric esters, phosphonic esters, sulfonic acids, which may optionally be in amine-blocked form, and tetraalkylammonium carboxylates.

14: The coating composition as claimed in claim 1, wherein catalysts C) are selected from the group consisting of amine-blocked phenyl phosphate, bis(2-ethylhexyl) phosphate, tetraethylammonium benzoate, tetrabutylammonium benzoate, and mixtures thereof.

15: The coating composition as claimed in claim 1.

16: In a process for producing coatings and paint systems, the improvement comprising including the coating composition as claimed in claim 1.

17: A substrate coated with at least one coating composition as claimed in claim 1.

Description

EXAMPLES

[0145] All percentages are based on weight, unless stated otherwise.

[0146] NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

[0147] All viscosity measurements were recorded with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219:1994-10 at a shear rate of 250 s-1.

[0148] The flow time was determined in accordance with DIN EN ISO 2431:2012-03 using an ISO flow cup with a 5 mm nozzle.

[0149] To produce automotive clearcoats, the polyols described below were in each case mixed, by intensive stirring at room temperature to form a homogeneous mixture, with a 10% solution of a customary leveling additive in butyl acetate (BYK 331; BYK-Chemie GmbH, Wesel, DE), the light stabilizers Tinuvin 292 and Tinuvin 384-2, each as a 50% solution in MPA, (BASF SE, Ludwigshafen, DE) and also, in the case of the formulations according to the invention from examples 2 and 4, tetraethylammonium benzoate (Sigma-Aldrich Chemie GmbH, Munich, DE) as a 50% solution in butanol as catalyst C). The respective polyisocyanates were stirred into this coating base component and the solids content of the complete coating composition was adjusted to a flow time of approximately 28 s with methoxypropyl acetate.

[0150] Table 1 shows the compositions of the individual formulations.

[0151] To determine the König pendulum damping (in accordance with DIN EN ISO 1522) and to test the solvent resistance, the coating compositions were each applied to glass plates using a gravity-fed cup gun and, after flashing off at room temperature for 10 minutes, cured at 140° C. within 22 minutes.

[0152] To test the coatings for solvent resistance, small amounts of each of the solvents xylene (X), 1-methoxy-2-propyl acetate (MPA), ethyl acetate (EA) and acetone (A) were placed in test tubes and provided with a cotton-wool pad at the opening, thus forming a solvent-saturated atmosphere within the test tubes. The test tubes were subsequently brought with the cotton-wool pad onto the surface of the coating film applied to glass, where they remained for 5 minutes. After the solvent had been wiped off, the film was examined for destruction/softening/loss of adhesion and rated (0=no change, 5=film completely dissolved). The evaluations reported are those for the four solvents in the order in each case of X, MPA, EA and A in the form of four successive digits.

[0153] The scratch resistance and also the resistance to fuels and chemicals were tested on the complete OEM multilayer construction on steel sheet.

[0154] For this purpose, the coating compositions were applied as clearcoats to cathodically electrocoated metal sheets using a gravity-fed cup gun, the metal sheets having been coated beforehand with a commercial 1K OEM waterborne primer-surfacer and with a conventional black 1K OEM waterborne basecoat. While the waterborne primer-surfacer was cured fully by baking at 165° C. for 20 minutes, the waterborne basecoat was merely subjected to preliminary drying at 80° C. for 10 minutes. Following the application of the clearcoats, the basecoat layer and the clearcoat layer were cured together at 140° C. over the course of 22 minutes.

[0155] Wet scratching was conducted using an Amtec-Kistler laboratory car wash in accordance with DIN EN ISO 20566, dry scratching was measured using a crockmeter and polishing paper in accordance with DIN 55654, Method A (cuboidal friction pin geometry, base area (22 mm×22 mm), testing force (22.0±0.5) N.

[0156] The gloss of the coatings obtained was measured by reflectometry to DIN EN ISO 2813 at the 200 angle.

[0157] The figure reported is the loss of gloss in Gloss Units (GU) after scratching (10 cycles). The lower the loss of gloss in GU, the more resistant the coating is to wet scratching.

[0158] A FAM test was conducted to measure the resistance to fuels. A small cotton-wool pad soaked with FAM solution according to DIN 51604-1 as the test substance was placed on the surface of the coating and covered with a watch glass to prevent evaporation. After an exposure period of 10 minutes, the cotton wool soaked with the test substance was removed, the exposed area was dried and immediately inspected visually and manually by touching and scratching. Softening and discoloration of the coating surface are assessed as follows:

[0159] 0=no changes; 1=swelling ring, hard surface, only visible change/traces of change in hue; 2=swelling ring, slight softening/slight change in hue; 3=distinct softening (possibly slight blistering)/medium change in hue/surface can be scratched; 4=significant softening (possibly severe blistering), can be scratched through to the substrate/significant change in hue; 5=coating completely destroyed without outside influence/very significant change in hue.

[0160] The chemical resistance test using a gradient oven was conducted in accordance with DIN EN ISO 2812-5:2007-05.

[0161] Table 2 shows a comparison of the results of the performance tests, each determined after a storage time of 24 h at 23° C.

[0162] Starting Compounds Used

[0163] Desmodur N 3390 BA/SN:

[0164] Aliphatic polyisocyanurate polyisocyanate based on HDI (Covestro Deutschland AG, Leverkusen), 90% solution in n-butyl acetate/solvent naphtha 100 (1:1), NCO content: 19.6%, viscosity at 23° C.: 550 mPas.

[0165] Silane-Functional Polyisocyanate P1:

[0166] 42.0 parts by weight of a commercial solvent-free polyisocyanurate polyisocyanate based on HDI (Desmodur N 3300, Covestro Deutschland AG, Leverkusen) with an NCO content of 21.8% and a viscosity at 23° C. of 3000 mPas were initially charged together with 36.0 parts by weight of n-butyl acetate at 25° C. and to this initial charge was added, within 120 min, a mixture of 2.0 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine and 20.0 parts by weight of bis[3-(trimethoxysilyl)propyl]amine. A polyisocyanate containing silane groups was obtained after a further stirring time of 30 min. The NCO content of the solution was 6.3%, the viscosity of the 64% solution was 90 mPas at 23° C.

[0167] Eastman Tetrashield IC3020:

[0168] Polyester polyol based on 2,2,4,4-tetramethylcyclobutane-1,3-diol (TMCD) (Eastman Chemical Company, Kingsport (Tenn.), US), 75% solution in n-butyl acetate, OH number (based on form as supplied): 150 mg KOH/g, viscosity at 23° C.: approximately 6000 mPas.

[0169] Setalux 91767 VX-60:

[0170] Sag control agent-modified polyacrylate polyol (Allnex Germany GmbH, Bitterfeld-Wolfen, DE), 60% solution in solvent naphtha/xylene (76/24), OH number (based on form as supplied): 90 mg KOH/g.

[0171] Setalux D A 665 BA/X

[0172] Polyacrylate polyol (Allnex Germany GmbH, Bitterfeld-Wolfen, DE), 65% solution in butyl acetate/xylene (75:25), OH number: 150 mg KOH/g (based on form as supplied), viscosity at 23° C.: approx. 2400 mPas.

TABLE-US-00001 TABLE 1 Clearcoat formulations. All figures in parts by weight unless otherwise stated. 1 3 5 Example (comparative) 2 (comparative) 4 (comparative) Component A Eastman Tetrashield IC3020 90.89 60.25 76.43 51.02 — Setalux 91767 VX-60 — — 23.89 15.84 26.11 Setalux D A 665 BA/X — — — — 96.41 Byk 331, 10% in BA 0.23 0.23 0.23 0.23 0.23 Tinuvin 292, 50% in MPA 2.30 2.30 2.30 2.30 2.30 Tinuvin 384-2, 50% in MPA 3.45 3.45 3.45 3.45 3.45 Tetraethylammonium benzoate, — 2.30 — 2.30 — 50% in butanol Methoxypropyl acetate (MPA) 48.76 22.34 44.64 20.03 29.89 Component B Desmodur N 3390 BA/SN 52.07 — 52.86 — 45.41 Polyisocyanate P1) — 109.13 — 111.54 — Methoxypropyl acetate (MPA) 10.50 — 5.00 — 41.68 Description Total parts by weight 208.20 200.0 208.8 206.81 245.48 NCO:OH 1:1 1:1 1:1 1:1 1:1 Solids content on application [%] 57.3 59.6 57.1 57.6 48.6

TABLE-US-00002 TABLE 2 Test results 1 3 5 Example (comparative) 2 (comparative) 4 (comparative) Tests on glass plate as per description Layer thickness on glass [μm] 51 50 46 51 44 Pendulum hardness [s] 212 209 214 213 204 Incipient solubility 5′ (X, (0-5) 0024 0000 0022 0001 0024 MPA, EA, A) Tests on the complete cathodic electrocoat/primer-surfacer/basecoat/clearcoat construction as per description FAM Test 10 min. (0-5) 2 1 1 1 2 Wet scratching Starting gloss 20° [GU] 86 88 88 88 90 Gloss after scratching 20° [GU] 47 74 55 74 62 Loss of gloss after 10 cycles Δ 39 14 33 14 28 Gloss after recovery for 2 h [GU] 51 77 59 77 81 at 60° C. 20° Residual gloss before [rel. %] 55 84 63 84 69 recovery Residual gloss after recovery [rel. %] 59 88 67 88 90 Dry scratching crockmeter (polishing paper) Starting gloss 20° [GU] 86 88 88 88 90 Gloss after scratching 20° [GU] 15 59 30 53 30 Loss of gloss after 10 cycles Δ 71 29 58 35 60 Gloss after recovery for 2 h [GU] 21 68 39 65 77 at 60° C. 20° Residual gloss before [rel. %] 17 67 34 60 33 recovery Residual gloss after recovery [rel. %] 24 77 44 74 86 Chemical resistance gradient oven Tree resin [° C.] 42 >68 52 >68 40 Pancreatin [° C.] 36 36 40 36 36 Distilled water [° C.] 49 50 62 64 >68 Sodium hydroxide solution, [° C.] 50 50 54 44 48 1% Sulfuric acid, 1% [° C.] 48 44 45 43 44

[0173] All coating materials cured to form hard, high-gloss coatings. Compared to the comparative coating material from example 5, which was formulated exclusively using polyacrylate polyols, all coating materials containing the polyester polyol based on 2,2,4,4-tetramethylcyclobutane-1,3-diol (examples 1 to 4, according to the invention and comparative) displayed improved chemical resistance. While the comparative coating materials from examples 1 and 3 crosslinked with the standard polyisocyanate had a significantly reduced scratch resistance compared to the TMCD-free comparative coaling material from example 5, the scratch resistance of the coating films according to the invention (examples 2 and 4), in particular in the case of wet scratching, was at a similarly high level as the standard 2K PUR coating material (example 5). The two coating films according to the invention displayed the lowest direct scratching (highest residual gloss before recovery) and by far the best solvent resistance and tree resin resistance, compared to all the comparative coating materials.