PROCESS FOR PRODUCING A MULTICOAT PAINT SYSTEM

Abstract

The present invention relates to a process for producing a multicoat paint system on a metallic substrate, by producing a basecoat film or two or more directly successive basecoat films directly on a metallic substrate coated with a cured electrocoat system, producing a clearcoat directly on the one or the topmost of the two or more basecoat films, and then jointly curing the one or the two or more basecoat films and the clearcoat film, and which comprises at least one basecoat material used in producing the basecoat films comprising at least one aqueous polyurethane-polyurea dispersion (PD) comprising polyurethane-polyurea particles, with the polyurethane-polyurea particles present in the dispersion (PD) comprising anionic groups and/or groups which can be converted into anionic groups, and having an average particle size of 40 to 2000 nm and also a gel fraction of at least 50%.

Claims

1. A process for producing a multicoat paint system (M) on a metallic substrate (S), the process comprising: (1) electrophoretically applying an electrocoat material (e.1) to a metallic substrate (S) and subsequent curing of the electrocoat material (e.1), to obtain a cured electrocoat (E.1) on the metallic substrate (S); (2) applying an aqueous basecoat material (b.2.1) directly to the cured electrocoat (E.1) or directly successively applying two or more basecoat materials (b.2.2.x) to the cured electrocoat (E.1), to obtain a basecoat film (B.2.1) or to obtain two or more directly successive basecoat films (B.2.2.x) directly on the cured electrocoat (E.1); (3) applying a clearcoat material (k) directly to the basecoat film (B.2.1) or a topmost basecoat film of the two or more directly successive basecoat films (B.2.2.x), to obtain a clearcoat film (K) directly on the basecoat film (B.2.1) or to obtain a topmost basecoat film (B.2.2.x) directly on the basecoat film (B.2.1); and (4) jointly curing the basecoat film (B.2.1) and the clearcoat film (K) or jointly curing the two or more directly successive basecoat films (B.2.2.x) and the clearcoat (K), to obtain a multicoat paint system (M) on the metallic substrate (S), wherein: the basecoat material (b.2.1) or at least one of the two or more basecoat materials (b.2.2.x) comprises at least one aqueous polyurethane-polyurea dispersion (PD) comprising polyurethane-polyurea particles; and the polyurethane-polyurea particles present in the dispersion (PD) comprise anionic groups, groups which can be converted into anionic groups, or both, and have an average particle size of 40 to 2000 nm and also a gel fraction of at least 50%.

2. The process as claimed in claim 1, wherein: the polyurethane-polyurea particles, in each case in reacted form, comprise (Z.1.1) at least one isocyanate group-containing polyurethane prepolymer comprising the anionic groups, the groups which can be converted into anionic groups, or both, and (Z.1.2) at least one polyamine comprising two primary amino groups and one or two secondary amino groups; and the dispersion (PD) comprises at least 90 wt % of the polyurethane-polyurea particles, and water.

3. The process as claimed in claim 1, wherein the anionic groups, the groups which can be converted into anionic groups, or both, are carboxylate group, carboxylic acid groups, or both.

4. The process as claimed in claim 2, wherein the polyamine (Z.1.2) comprises one or two secondary amino groups, two primary amino groups, and aliphatically saturated hydrocarbon groups.

5. The process as claimed in claim 1, wherein the polyurethane-polyurea particles present in the dispersion (PD) have an average particle size of 110 to 500 nm and a gel fraction of at least 80%.

6. The process as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one of the two or more basecoat materials (b.2.2.x) further comprises at least one hydroxy-functional polymer as binder, said at least one hydroxy-functional polymer selected from the group consisting of a polyurethane, a polyester, a polyacrylate and copolymers thereof.

7. The process as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one of the two or more basecoat materials (b.2.2.x) is a one-component coating material.

8. The process as claimed in claim 1, wherein the joint curing (4) is carried out at temperatures of 100 to 250? C. for a duration of 5 to 60 min.

9. The process as claimed in claim 1, wherein at least two directly successive basecoat films (B.2.2.x) are produced, said basecoat films (B.2.2.x) comprising a first basecoat film (B.2.2.a) directly on the cured electrocoat (E.1) comprising at least one white pigment and at least one black pigment, and at least one further basecoat film (B.2.2.x) comprising at least one effect pigment.

10. The process as claimed in claim 1, wherein: when the basecoat material (b.2.1) and the two or more basecoat materials (b.2.2.x) comprise at least one crosslinking agent, they have a solids content of at least 25%; and when the basecoat material (b.2.1) and the two or more basecoat materials (b.2.2.x) contain no crosslinking agent, they have a solids content of at least 15%.

11. The process as claimed in claim 10, wherein the basecoat materials (b.2.1) and (b.2.2.x) have a viscosity of 40 to 150 mPa.Math.s at 23? C. under a shearing load of 1000 l/s.

12. The process as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one of the basecoat materials (b.2.2.x), comprises at least one crosslinking agent selected from the group consisting of the a blocked polyisocyanate and an aminoplast resin.

13. The process as claimed in claim 2, wherein the prepolymer (Z.1.1) comprises at least one polyester diol prepared from diols and dicarboxylic acids, with at least 50 wt of the dicarboxylic acids being dimer fatty acids.

14. The process as claimed in claim 1, wherein the basecoat material (b.2.1) or the two or more basecoat materials (b.2.2.x) are applied to the cured electrocoat (E.1) by electrostatic spray application or pneumatic spray application.

15. A multicoat paint system (M) produced by the process of claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0341] FIG. 1:

[0342] Schematic construction of a multicoat paint system (M) of the invention disposed on a metallic substrate (S), the system (M) comprising a cured electrocoat (E.1) and also a basecoat film (B.2.1) and a clearcoat film (K) which have been jointly cured.

[0343] FIG. 2:

[0344] Schematic construction of a multicoat paint system (M) of the invention disposed on a metallic substrate (S), the system (M) comprising a cured electrocoat (E.1), two basecoat films (B.2.2.x), namely a first basecoat film (b.2.2.a) and a topmost basecoat film (b.2.2.z) disposed over it, and a clearcoat film (K), which have been jointly cured.

[0345] FIG. 3:

[0346] Schematic construction of a multicoat paint system (M) of the invention disposed on a metallic substrate (S), the system (M) comprising a cured electrocoat (E.1), three basecoat films (B.2.2.x), namely a first basecoat film (b.2.2.a), a basecoat film (b.2.2.b) disposed over it, and a topmost basecoat film (b.2.2.z), and also a clearcoat film (K), which have been jointly cured.