Process for the production of a dark-color multi-layer coating
A process for the production of a dark-color multi-layer coating, comprising the successive steps: (1) applying an NIR-opaque coating layer A′ from a pigmented, solvent- or waterborne coating composition A to a substrate, (2) applying a coating layer B′ from a pigmented coating composition B onto the substrate provided with coating layer A′, wherein the pigment content of coating composition A consists 90 to 100 wt. % of at least one aluminum flake pigment and 0 to 10 wt. % of at least one further pigment, which is selected in such a way that NIR-opaque coating layer A′ exhibits low NIR absorption, wherein the pigment content of coating composition A comprises <90 wt. % of 10 to 80 nm thick aluminum flake pigments, wherein the pigment content of coating composition B consists 50 to 100 wt. % of at least one black pigment with low NIR absorption and 0 to 50 wt. % of at least one further pigment, which is selected in such a way that coating layer B′ exhibits low NIR absorption and that the dark-color multi-layer coating exhibits a brightness L* (according to CIEL*a*b*, DIN 6174), measured at an illumination angle of 45 degrees to the perpendicular and an observation angle of 45 degrees to the specular, of at most 10 units, wherein the sum of the respective wt. % equals 100 wt. %, and wherein the coating layers A′ and B′ are cured.
1. A process for the production of a dark-color multi-layer coating, comprising the successive steps:
(1) applying an NIR-opaque coating layer A′ from a pigmented, solvent- or waterborne coating composition A to a substrate,
(2) applying a coating layer B′ from a pigmented coating composition B onto the substrate provided with coating layer A′,
wherein the pigment content of coating composition A consists 90 to 100 wt. % of at least one aluminum flake pigment and 0 to 10 wt. % of at least one further pigment, and the pigment content of coating composition A is selected in such a way that NIR-opaque coating layer A′ exhibits an NIR reflection of at least 48% over the entire NIR wavelength range of 780 to 2100 nm,
wherein the pigment content of coating composition A comprises <90 wt. % of 10 to 80 nm thick aluminum flake pigments,
wherein the pigment content of coating composition B consists 50 to 100 wt. % of at least one black pigment with low NIR absorption and 0 to 50 wt. % of at least one further pigment, and the pigment content of coating composition B is selected in such a way that coating layer B′ exhibits low NIR absorption and that the dark-color multi-layer coating exhibits a brightness L* (according to CIEL*a*b*, DIN 6174), measured at an illumination angle of 45 degrees to the perpendicular and an observation angle of 45 degrees to the specular, of at most 10 units,
wherein the sum of the respective wt. % equals 100 wt. %, and
wherein the coating layers A′ and B′ are cured.
2. The process of claim 1 , wherein the pigment content of coating composition A consists exclusively of the at least one aluminum flake pigment.
3. The process of claim 1 , wherein coating composition A does not contain any carbon black.
4. The process of any one of the preceding claims, wherein the at least one black pigment with low NIR absorption is selected from the group consisting of iron oxide black pigments, mixed metal/iron oxide black pigments and perylene black pigments.
5. The process of claim 1 , wherein coating composition B does not contain any carbon black.
6. The process of claim 1 , wherein coating layer B′ is a transparent or a visually opaque coating layer.
7. The process of claim 1 comprising a further successive step (3) of application and curing of a clear coat.
8. The process of claim 7 , wherein coating layer A′ is cured in step (1) and coating layer B′ and the clear coat layer applied in step (3) are jointly cured.
9. The process of claim 7 , wherein coating layers A′, B′ and the clear coat layer applied in step (3) are jointly cured.
10. A substrate provided with a dark-color multi-layer coating produced by the process of claim 1 .