AQUEOUS PRIMER COATING

Abstract

The present invention relates to novel coatings which are applied from an aqueous phase to substrates such as plastics, and which are overlaid with other coatings. These coatings are characterized by particularly good adhesive strength, in particular on plastics, and are thus particularly commercial.

Claims

1. A composition for coating substrates, comprising at least one optionally hydroxy-functional, anionic or nonionic polyurethane dispersion and at least one anionic styrene-butadiene copolymer dispersion.

2. The composition as claimed in claim 1, wherein a weight ratio of the at least one polyurethane dispersion to the anionic styrene-polybutadiene copolymer dispersion is in a range from 10:1 to 1:3, based on a nonvolatile proportion of the composition.

3. The composition as claimed in claim 1, wherein the composition comprises the at least one polyurethane dispersion in an amount of from 33 to 90% by weight, based on a nonvolatile proportion of the composition.

4. The composition as claimed in claim 1, wherein the composition comprises the at least one anionic styrene-polybutadiene copolymer dispersion in an amount of from 9 to 67% by weight, based on a nonvolatile proportion of the composition.

5. The composition as claimed in claim 1, wherein the composition comprises at least one reactive crosslinker component.

6. The composition as claimed in claim 5, wherein the at least one reactive crosslinker component comprises a polyisocyanate having a functionality in a range from 1.5 to 6.

7. The composition as claimed in claim 1, wherein the polyurethane dispersion comprises a polyurethane obtained from a reaction of reaction mixture comprising: (A) at least one diol and/or polyol component, (B) at least one polyisocyanate component, (C) at least one hydrophilizing component having at least one hydrophilizing group, (D) optionally mono-, di-, or tri-amino-functional compounds, or a combination thereof and/or hydroxyamino-functional compounds, and (E) optionally at least one additional isocyanate-reactive compound.

8. The composition as claimed in claim 7, wherein the polyol component (A) has a number average molecular weight Mn in a range from 62 to 18 000 g/mol.

9. The composition as claimed in claim 7, wherein the at least one polyisocyanate component (B) comprises tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3, 3, 5-trim ethyl-5-isocyanato-methylcyclohexane, 4,4′-diisocyanato-dicyclohexylmethane, bis(4-isocyanatocyclohexyl)methane, 2,2-bis(4-isocyanatocyclohexyl)propane, 1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 2,2′-diisocyanatodiphenylmethane, and-2,4′-diisocyanatodiphenylmethane, tetramethyl-xylylene diisocyanate, p-xylylene diisocyanate, p-isopropylidene diisocyanate or a mixture of at least two of these compounds.

10. The composition as claimed in claim 7, wherein the hydrophilizing group of the hydrophilizing component (C) comprises a sulfonate group, a carboxylate group, or a combination thereof.

11. The composition as claimed in claim 7, wherein the mono-, di-, or tri-amino-functional compounds and/or hydroxyamino-functional compounds (D) comprise aliphatic, alicyclic primary, secondary monoamines, or a combination thereof.

12. The composition as claimed in claim 7, wherein the composition comprises at least one electrically conductive pigment.

13. A method of coating a substrate, comprising applying the composition as claimed in claim 1 to at least of portion of the substrate.

14. A multilayer structure, comprising at least the composition as claimed in claim 1.

15. An object, comprising a substrate coated with the composition as claimed in claim 1.

16. The composition as claimed in claim 5, wherein the at least one reactive crosslinker component comprises a polyisocyanate in an amount of from 0.01 to 5% by weight, based on a nonvolatile proportion of the composition.

17. The composition as claimed in clam 6, wherein the at least one reactive crosslinker component comprises the polyisocyanate in an amount of from 30 to 100% by weight, based on a total mass of the at least one reactive crosslinker component.

18. The composition as claimed in claim 8, wherein the polyol component (A) comprises a polyether polyol, a polyester polyol, a polycarbonate polyol, a polylactone polyol, a polyamide polyol, or mixtures of at least two thereof.

19. The composition as claimed in claim 12, wherein the composition comprises the at least one electrically conductive pigment in an amount of from 0.01 to 10% by weight, based on a total weight of the composition.

Description

Experimental Part

[0104] The invention will be further illustrated below with the aid of examples.

Substances Used:

[0105] The substances were, unless indicated otherwise, used without purification or pretreatment. Bayhydrol® U 2757, Covestro AG, DE, aliphatic, anionic hydroxy-functional polyurethane dispersion based on a mixture of an aromatic polyester diol and a polycarbonate diol, cosolvent-free. Binder for producing water-dilutable two-component PUR coatings, about 52% strength in water/ N,N-dimethylethanolamine, hydroxyl content about 1.8% (calculated) based on the nonvolatile proportion (1 g/1 h/125° C.) in accordance with DIN EN ISO 3251, specifications as per datasheet issued on Sep. 1, 2015.

[0106] Bayhydrol® UH 2606, Covestro AG, DE, aliphatic, polycarbonate-containing anionic polyurethane dispersion, cosolvent-free. Binder for producing water-dilutable coatings for plastic substrates and wood materials, about 35% strength in water, neutralized with N-ethyldiisopropylamine (bound as Salt) in the ratio of about 35:64:1, specifications as per datasheet issued on 09/01/2015.

[0107] Desmodur® N 3600, Covestro AG, DE, polyisocyanate based on trimers of hexamethylene diisocyanate, NCO content 23.0% (ISO 11909), viscosity 1200 mPa s at 23° C.(ISO 3219/A.3), specifications as per datasheet issued on Jun. 1, 2017.

[0108] Bayhydur® XP 2655, Covestro AG, DE, hydrophilic polyisocyanate based on trimers of hexamethylene diisocyanate, NCO content 20.8% (ISO 11909), viscosity 3500 mPa s at 23° C.(ISO 3219/A.3), specifications as per datasheet issued on Jun. 1, 2017.

[0109] Litex® SX 1024, Synthomer Deutschland GmbH, aqueous colloidal dispersion of a styrene-butadiene copolymer having carboxyl groups, containing an anionic emulsifier system, stabilized with an antioxidant. Solids content 50.0%, pH 7,0, viscosity <400 mPas, glass transition temperature −15° C., average particle size 0.15 μm, specifications as per Technical Data Sheet, Revision: 3, Oct. 30, 2014.

[0110] Litex® S 7140, Synthomer Deutschland GmbH, aqueous, anionic dispersion of a carboxylated styrene-butadiene copolymer, stabilized with a noncoloring antioxidant. Solids content 51.0%, pH 8.0, viscosity <300 mPas, glass transition temperature 48° C., average particle size 190 nm, specifications as per Technical Data Sheet, Revision: 4, Oct. 30, 2014.

[0111] Litex® S 7155, Synthomer Deutschland GmbH, anionic dispersion of carboxylated styrene-butadiene copolymer, stabilized with a noncoloring antioxidant. Solids content 50.0% pH 7.75, viscosity <750 mPas, glass transition temperature −26 ° C., average particle size 195 nm, specifications as per Technical Data Sheet, Revision: 4, Oct. 30, 2014.

[0112] Litex® PX 9306, Synthomer Deutschland GmbH, aqueous, anionic, carboxylated dispersion of a styrene-butadiene copolymer. Solids content 50.0%, pH 6,7, viscosity <300 mPas, glass transition temperature 12° C., specifications as per Technical Data Sheet, Revision: 4, Oct. 30, 2014.

[0113] Dispex® Ultra FA 4436, BASF SE, DE, dispersant

[0114] Surfynol® 104 E, Evonik Resource Efficiency GmbH, DE, nonionic wetting agent, antifoam dispersant

[0115] Byk® 348, Byk Chemie GmbH, DE, silicone surfactant for improving wetting of the substrate

[0116] R-KB-2, Sachtleben Chemie GmbH, white pigment

[0117] Blanc fixe micro, Sachtleben Chemie GmbH, filler

[0118] Finntalc® M-15 AW, Mondo Minerals B.V., NL, talc

[0119] Bayferrox0 318 M, Lanxess AG, DE, iron oxide pigment

[0120] Aerosil® R 972, Evonik Resource Efficiency GmbH, DE, pyrogenic silica

[0121] N,N-dimethylethanolamine (DMEA), Aldrich, DE, neutralizing agent

[0122] Borchigel® PW 25, OMG Borchers, DE, polyurethane thickener

[0123] 1-methoxy-2-propyl acetate (MPA), BASF SE, DE, solvent

[0124] Hydrobasislack schwarz R 2341, Karl Worwag Farben- und Lackfabrik GmbH&Co KG, DE, black aqueous base coating, in particular being suitable for plastic substrates provided with a primer.

[0125] Woeropur Klarlack R 3209, Karl Worwag Farben- und Lackfabrik GmbH&Co KG, DE, solvent-based two-component polyurethane coating consisting of stock coating composition and hardener for coating plastics substrates, in particular for coating over Hydrobasislack R 2341.

Plastics Substrates:

[0126] The following thermoplastics were used in the form of rectangular test plates (having a size of at least 13×18 cm). In addition, a polycarbonate film was used as substrate. All plates and films were wiped with a clean cloth soaked with ethyl acetate before coating. [0127] 1. Bayblend® T65 XF: polycarbonate-polyacrylonitrile-polybutadiene-polystyrene copolymer blend [PC/ABS], Covestro AG, DE [0128] 2. Pocan T 7323: polybutylene terephthalate-polyethylene terephthalate copolymer blend containing 20% glass fibers [PBT+PET], Lanxess Deutschland GmbH, DE [0129] 3. Durethan BKV 30 H2.0 OEF: polyamide 6 containing 30% glass fibers [PA6], Lanxess Deutschland GmbH, DE [0130] 4. Durethan BKV 60 H2.0 OEF: polyamide 6 containing 30% glass fibers [PA6], Lanxess Deutschland GmbH, DE [0131] 5. Makrofol DE 1-1 CG 000000, polycarbonate film having a layer thickness of 500 p.m

[0132] [PC], Covestro AG, DE

Test Methods:

[0133] 1. Time taken to run out from a 4 mm DIN cup in accordance with DIN EN ISO 2431:2012 [0134] 2. Testing of the adhesive strength of a coating on a substrate by means of a cross-cut test using a multiblade tool with handle in accordance with DIN EN ISO 2409:2013 (blade spacing 1 mm only for the primer layer to 2 mm for a multilayer structure of primer, base coating, clear varnish): after carrying out cross-cuts down to the substrate, loose particles were removed using a brush. A “Scotch Pressure Sensitive Tape” adhesive tape from 3M was then firstly rubbed onto the cut lattice pattern by means of a thumb nail and quickly pulled off as vertically as possible in an upward direction from the coating. The damage was evaluated using a magnifying glass and evaluated by comparison with the cut patterns depicted in the standard. GT 0 means that the cut patterns are completely smooth and no pieces have flaked off. [0135] 3. Steam jet test in accordance with DIN EN ISO 16925:2014 on plastic parts coated with a primer and a topcoat: the test was carried out by the method A 3.9 using a Sikkens scoring tool and a steam jet instrument from Walther. The parts were conditioned at 23±2° C. and 50±5% atmospheric humidity for at least 16 hours before the test. At characteristic values of KW 0 and KW 1, the test is considered to have been passed; at KW 2, it is considered to have been conditionally passed and at KW 3 to 5 it has not been passed. A lowercase letter (a, b or c) after the characteristic value 1 or 2 serves for a more detailed explanation of the damage pattern as indicated in the standard.

Surface Coating Formulations:

[0136] The following surface coating formulations (table 1) were produced as follows. Comparative example 1[V] corresponded to the starting formulation disclosed by Covestro AG, DE for aqueous, two-component plastic primer PCO-0148-PS (edition Sep. 13, 2016). To produce all of the surface coating formulations of table 1, the binders (part 1) were in each case initially charged and the constituents under part 2 were weighed in, in the order indicated, and mixed with glass beads (2.85 3.45 mm) 1:1 (by volume) and made into a paste using a laboratory shaker Skandex BA-S20 from Lau for 30 minutes. The glass beads were subsequently sieved off. The thickener (part 3) was subsequently introduced slowly into the cooled surface coating while stirring by means of a high-speed stirrer (stirrer disk 5 cm, at 800 rpm) and the mixture was subsequently stirred for a further 5 minutes. The formulated dispersed surface coatings were adjusted by means of deionized water to a running-out time from a 4 mm DIN cup of from 25 to 30 s. Table 1 shows the amount of water necessary for this in each case under part 4. Shortly before application, part 5 was incorporated while stirring with a blade stirrer (5 min, 700 rpm). The running-out time from a 4 mm cup was subsequently determined and the primers were applied within 30 minutes.

TABLE-US-00001 TABLE 1 Surface coating formulations for primer (1[V])- comparison, 2 to 7 - according to the invention) 1[V] 2 3 4 5 6 7 Part 1 Bayhydrol ® U 2757 79.1 55.1 55.1 55.1 55.1 51.5 51.6 Bayhydrol ® UH 124.3 86.6 86.6 86.6 86.6 153.0 76.7 2606 Litex ® SX 1024 — 60.6 — — — 53.6 107.3 Litex ® S 7140 — — 59.4 — — — — Litex ® S 7155 — — — 60.6 — — — Litex ® PX 9306 — — — — 60.6 — — Part 2 Dispex ® Ultra FA 1.6 1.6 1.6 1.6 1.6 1.9 1.9 4436 Surfynol ® 104 E 1.0 1.0 1.0 1.0 1.0 0.8 0.8 Byk ® 348 0.7 0.7 0.7 0.7 0.7 1.2 1.2 R-KB-2 30.0 30.0 30.0 30.0 30.0 52.1 52.1 Blanc fixe micro 45.0 45.0 45.0 45.0 45.0 34.7 34.7 Finntalc ® M-15 AW 15.0 15.0 15.0 15.0 15.0 17.4 17.4 Bayferrox ® 318 M 1.0 1.0 1.0 1.0 1.0 1.2 1.2 Aerosil ® R 972 2.6 2.6 2.6 2.6 2.6 3.0 3.0 DMEA (10% strength — — — — — — — in water) Water 30 55 40 40 35 30 50 Part 3 Borchigel ® PW 25 0.7 0.7 0.7 0.7 0.7 0.8 0.8 Part 4 Water for setting to 36.8 60.8 36.5 46.9 35.7 34.9 57.5 25-30 s running out time Part 5 Desmodur ® N 3600: 17.3 12.1 12.1 12.1 12.1 11.3 11.3 Bayhydur ® XP 2655 (70:30) 75% strength in MPA Overall total 385.1 427.9 387.3 398.9 382.7 448.4 467.5 Calculated nonvolatile 51.2 46.1 50.9 49.4 51.5 50.9 48.8 proportion [%] Measured running-out 25 26 24 22 24 24 24 time [s] Calculated molar ratio 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 1.5:1 of NCO:OH 100 g total parts 1-3 4.7 2.9 3.2 3.1 3.3 2.6 2.5 to x g of part 4
Application of Surface Coating To test the adhesive strength before and after storage under hydrolysis conditions of 90° C., 90% relative atmospheric humidity for 72 hours, the primer in the form of the surface coating compositions 1C, 2 to 7 was applied over the full area of the plastics substrates and dried. Half of the area was subsequently covered and the other half was coated with black Hydrobasislack R 2341 and then with Klarlack R 3209. The adhesive strength of the primer and the total structures of primer, base coat and clear varnish was, in each case after aging of the coated plates, 16 hours at 60° C. in a convection oven and 8 hours at room temperature, tested by means of the cross-cut test (1 mm blade spacing for the primer, 2 mm spacing for the total structures) both before and after storing under hydrolysis conditions.

[0137] For testing of the adhesive strength by the steam jet test, the plastics substrates of Bayblend® were in each case coated over their full area firstly with the primers and then with base coating and clear varnish. Testing was in each case carried out after aging of the coated plates for 16 hours and 60° C. in a convection oven and subsequent conditioning in a standard atmosphere.

[0138] In both test series, the application of the primer was carried out using a flow cup gun Satajet RP, 1.3 mm, air pressure 2.1 bar in 1 cross pass in order to produce a layer thickness (dry) of 20-25 gm. After application, the primer was dried for 10 minutes at room temperature, for 30 minutes at 80° C. in a convection oven and stored for 16 hours at room temperature.

[0139] Application of the base coating was carried out using a flow cup gun Satajet HVLP, 1.2 mm, air pressure 2.1 bar in one cross pass in order to produce a layer thickness (dry) of 9-12 gm. The base coating was dried for 10 minutes at room temperature, for 30 minutes at 80° C. in a convection oven and stored for 3 hours at room temperature. Application of the clear varnish was carried out after mixing stock coating composition and hardener according to the manufacturer's instructions by means of a flow cup gun Satajet HVLP, 1.2 mm, air pressure 2.1 bar in 1 cross pass in order to produce a layer thickness (dry) of 25-32 gm. The clear varnish was dried for 10 minutes at room temperature and for 45 minutes at 80° C. in a convection oven. It was subsequently stored at 60° C. for 16 hours.

[0140] Results of cross-cut test before and after storage under hydrolysis conditions All primers (1[V], 2 7) and all total structures composed of primer (1[V], 2 7), base coating and clear varnish displayed excellent initial adhesion (all GT 0) and unaltered adhesive strength after storage under hydrolysis conditions (all GT 0) and after regeneration (all GT 0) on all plastics substrates tested (Bayblend®, Pocan®, both Durethan® grades and Makrofol®).

[0141] This result shows that, despite a proportion of cheaper binders, the primer formulations according to the invention are just as suitable for producing primers having excellent adhesive strength as the comparable example (1[V]) which contains only binders based on polyurethanes.

Results of Steam Let Test

[0142]

TABLE-US-00002 TABLE 2 Results of the steam jet test on Bayblend ® plates coated with primer, base coating and clear varnish (primer 1[V] - comparison 2 to 7 - according to the invention). 1[V] 2 3 4 5 6 7 Characteristic values 2a 2a 2a 2a 1a 1c 1c Evaluation Conditional Conditional Conditional Conditional OK OK OK

[0143] The results of the steam jet test show that the surface-coated plastic plates with the primers according to the invention have at least the same resistance after stressing with the steam jet as the comparative example (1[V]) which contains only binders based on polyurethanes.