USE OF LOW-MOLECULAR CARBOXYLIC ACIDS IN AQUEOUS BASE COATS

Abstract

Described herein is a method of using aromatic and/or araliphatic carboxylic acids in preparation of aqueous basecoat materials for the purpose of improving the adhesion of the aqueous basecoat materials to overbaked clearcoat materials. Also described herein is a method for producing a multicoat paint system, where a basecoat material is applied directly to an overbaked clearcoat film.

Claims

1. A method of using aromatic and araliphatic carboxylic acids, the method comprising using the carboxylic acids in preparation of aqueous basecoat materials for the purpose of improving the adhesion of the aqueous basecoat materials to overbaked clearcoat materials.

2. The method as claimed in claim 1, wherein the carboxylic acids are monocarboxylic acids.

3. The method as claimed in claim 1, wherein the basecoat materials contain 0.1 to 5 wt % of aromatic and/or araliphatic carboxylic acids, based on a total amount of the respective aqueous basecoat materials.

4. The method as claimed in claim 1, wherein the basecoat materials contain 0.3 to 1.5 wt % of aromatic and/or araliphatic carboxylic acids, based on a total amount of the respective aqueous basecoat materials.

5. The method as claimed in claim 1, wherein the carboxylic acids contain 7 to 15 carbon atoms.

6. The method as claimed in claim 1, wherein the basecoat materials comprise at least one hydroxy-functional polymer as binder, wherein the hydroxy-functional polymer is selected from the group consisting of polyurethanes, polyesters, poly(meth)acrylates and/or copolymers of the stated polymers.

7. A method for producing a multicoat paint system on a substrate, wherein (1) a substrate coated with a cured multicoat paint system is provided, wherein a topmost coat of the multicoat paint system is an overbaked clearcoat, (2) an aqueous basecoat material comprising at least one aromatic and/or araliphatic carboxylic acid is applied directly to the overbaked clearcoat from stage (1), and a basecoat polymer film is formed from the applied basecoat material, (3) a clearcoat material is applied to the basecoat polymer film obtained under stage (2), and subsequently (4) the basecoat polymer film from stage (2) and the clearcoat film from stage (3) are cured together.

8. The method as claimed in claim 7, wherein the method further comprises a stage (2a) between the stages (2) and (3), in which directly atop the basecoat polymer film obtained under stage (2) at least one further basecoat material is applied and a topmost basecoat polymer film is formed from the at least one further basecoat material, with a clearcoat material then being applied in stage (3) directly atop the basecoat polymer film or the topmost basecoat polymer film produced in stage (2a), and subsequently, in stage (4), the basecoat polymer films from stages (2) and (2a) and the clearcoat film from stage (3) are cured together.

9. The method as claimed in claim 7, wherein the substrate is a metallic or plastics substrate.

10. The method as claimed in claim 7, wherein the overbaked clearcoat from stage (1) represents a topmost coat of a multicoat paint system exhibiting defects.

11. A multicoat paint system on a substrate, produced by a method as claimed in claim 7.

12. The method as claimed in claim 5, wherein the carboxylic acids contain 7 to 8 carbon atoms.

Description

EXAMPLES OF PAINT FORMULATIONS

[0046] With regard to the formulating constituents and amounts thereof indicated in the tables hereinafter, the following should be taken into account. Where reference is made to a commercial product or to a production protocol described elsewhere, the reference, irrespective of the particular principal designation selected for the constituent is to exactly that commercial product or exactly the product produced by the protocol referenced.

[0047] Accordingly, where a formulating constituent is given the principal identification melamine-formaldehyde resin and where a commercial product is specified for it, the melamine-formaldehyde resin is used in the form of exactly that commercial product. Any further constituents present in the commercial product, such as solvents, must therefore be taken into account if the aim is to deduce the amount of the active substance (the melamine-formaldehyde resin).

[0048] Accordingly, where a formulation constituent is referenced using a production protocol and where such production results, for example, in a polymer dispersion having a defined solids content, it is exactly this dispersion which is used. It does not matter whether the principal identification selected is the term polymer dispersion or only the active substance, as for example polymer, polyester or polyurethane-modified polyacrylate. This should be borne in mind if the intention is to deduce the amount of the active substance (the polymer).

[0049] All of the proportions indicated in the tables are parts by weight.

[0050] 1. Production of a Non-Inventive Waterborne Basecoat Material 1

[0051] The components listed under aqueous phase in table A were stirred together in the order stated to form an aqueous mixture. In the next step an organic mixture was prepared from the components listed under organic phase. The organic mixture was added to the aqueous mixture. The combined mixture was then stirred for 10 minutes and adjusted, using deionized water and dimethylethanolamine, to a pH of 8 and to a spray viscosity of 115 mPas under a shearing load of 1000 s.sup.1 as measured with a rotary viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at 23 C.

TABLE-US-00001 TABLE A Waterborne basecoat material 1 Parts by Component weight Aqueous phase 3% NaMg phyllosilicate solution 13.8 Deionized water 13.72 Butyl glycol 1.4 Polyurethane-modified polyacrylate; prepared as per page 7 2.8 line 55 to page 8 line 23 of DE 4437535 A1 50% by weight solution of Rheovis PU 1250 (BASF), 0.53 rheological agent, in butyl glycol 10% by weight aqueous Rheovis AS1130 solution; 4.8 rheological agent, available from BASF, in water Polyester; prepared as per EP 12182050, page 28, lines 13-33 2 Polyester; prepared as per example D, column 16 lines 37-59 1.43 of DE-A-4009858 Melamine-formaldehyde resin (Luwipal 052 from BASF SE) 1.9 Melamine-formaldehyde resin (Resimene HM2608 052 4.7 from lneos) 10% dimethylethanolamine in water 1.2 Polyurethane; prepared in analogy to EP 1358278 B1 (page 11.5 14 - lines 38-53) Isopropanol 1.3 2-Ethylhexanol 1 n-Butoxypropanol 1 Triethylene glycol 1.28 Isopar L from Exxon Mobil 3 Byk-347 from Altana 0.53 Pluriol P 900 from BASF SE 0.7 Tinuvin 1130 from BASF SE 2.24 Red paste 15.5 Blue paste 0.43 Interference pigment suspension Mearlin Ext. super red 0.2 Mixing varnish, prepared in analogy to EP 1534792 B1, 0.6 column 11, lines 1-17 Organic phase Aluminum pigment 1, available from Altana-Eckart 0.23 Aluminum pigment 2, available from Altana-Eckart 0.1 Paliocrome Orange from BASF SE 3.56 Butyl glycol 4.66 Mixing varnish, prepared in analogy to EP 1799783 A1, page 3.89 7, lines 40-47

[0052] Production of the Blue Paste:

[0053] The blue paste was produced from 69.8 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 12.5 parts by weight of Paliogen Blue L 6482, 1.5 parts by weight of dimethylethanolamine (10% in demineralized water), 1.2 parts by weight of a commercial polyether (Pluriol P900 from BASF SE) and 15 parts by weight of deionized water.

[0054] Production of the Red Paste:

[0055] The red paste was produced from 40 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 34.5 parts by weight of Cinilex DPP Red, 2 parts by weight of a commercial polyether (Pluriol P900 from BASF SE), 3 parts by weight of 1-propoxy-2-propanol and 20.5 parts by weight of deionized water.

[0056] 2. Production of a Waterborne Basecoat Material I1 of the Invention

[0057] The waterborne basecoat material I1 was prepared in analogy to table A, but with further addition of 8 parts by weight of a mixture of 14.06 parts by weight of benzoic acid (from IMCD Deutschland GmbH & Co. KG) and 102.4 parts by weight of a 10% dimethylethanolamine solution in deionized water.

[0058] 3. Production of a Waterborne Basecoat Material I2 of the Invention

[0059] The waterborne basecoat material I2 was prepared in analogy to table A, but with further addition of 6.4 parts by weight of a mixture of 14.5 parts by weight of benzoic acid, 13.6 parts by weight of a 15% ammonia solution in deionized water and 66.6 parts by weight of deionized water.

[0060] 4. Production of a Waterborne Basecoat Material I3 of the Invention

[0061] The waterborne basecoat material I3 was prepared in analogy to table A, but with further addition of 8.1 parts by weight of a mixture of 15.67 parts by weight of para-toluic acid (CAS No.: 99-94-5 from Sigma-Aldrich) and 102.4 parts by weight of a 10% dimethylethanolamine solution in deionized water.

[0062] 5. Production of a Waterborne Basecoat Material I4 of the Invention

[0063] The waterborne basecoat material I4 was prepared in analogy to table A, but with further addition of 8.1 parts by weight of a mixture of 15.67 parts by weight of ortho-toluic acid (CAS No.: 118-90-1 from Sigma-Aldrich) and 102.4 parts by weight of a 10% dimethylethanolamine solution in deionized water.

[0064] Comparison Between Waterborne Basecoat Materials 1 and I1 to I4

[0065] To determine the cross-cut resistance, multicoat paint systems were produced according to the following general protocol:

[0066] A steel sheet coated with a cured cathodic electrocoat system, and with dimensions of 1020 cm, served as the substrate.

[0067] This metal sheet was first coated with the waterborne primer-surfacer SecuBloc MB 7 245, available commercially from BASF Coatings GmbH, applied in a dry film thickness of about 20 m, and this coating was subjected to interim drying at a temperature of 70 C. over a period of 10 minutes. Applied subsequently to the interim-dried waterborne primer-surfacer film were the waterborne basecoat materials 1 and I1 to I4, in a dry film thickness of 25 m; after 4 minutes of flashing at room temperature and also interim drying at 70 C. over 10 minutes, these basecoats were coated with the two-component clearcoat material Igloss from BASF Coatings GmbH, applied in a dry film thickness of 40 m. The resulting clearcoat film was flashed off at room temperature for 20 minutes. The waterborne basecoat film and the clearcoat film were subsequently cured in a forced air oven at 150 C. for 68 minutes to give a substrate coated with a multicoat paint system, the topmost coat of the multicoat paint system being an overbaked clearcoat.

[0068] The waterborne basecoat material 1 and, respectively, I1 to I4 were subsequently applied to the above-described original finish (multicoat paint system), in a dry film thickness of about 25 m. After the basecoat material had been flashed off at room temperature for 4 minutes, it was subjected to interim drying in a forced air oven at 70 C. for 10 minutes. Applied atop the interim-dried waterborne basecoat film was the two-component clearcoat material Igloss from BASF Coatings GmbH, in a dry film thickness of about 40 m. The resulting clearcoat film was flashed off at room temperature for 20 minutes. The waterborne basecoat film and the clearcoat film were then cured in a forced air oven at 140 C. for 20 minutes to give a multicoat paint system.

[0069] The multicoat paint systems thus obtained were examined for cross-cut adhesion. For this purpose, the cross-cut was conducted to DIN EN ISO 2409:2013-6. The results of the cross-cut test were assessed according to DIN EN ISO 2409:2013-6. Low result scores denote improved adhesion.

[0070] The results can be found in table 1.

TABLE-US-00002 TABLE 1 Cross-cut resistance of the systems comprising waterborne basecoat materials 1 and l1 to l4 WBM system Cross-cut result Assessment 1 5 unsatisfactory l1 0 satisfactory l2 1 satisfactory l3 0 satisfactory l4 0 satisfactory

[0071] The results emphasize that the use of specific carboxylic acids in waterborne basecoat materials results in a significant increase in the cross-cut resistance (i.e., in the intercoat adhesion) in comparison to waterborne basecoat material 1.