Dark-Color Multi-Layer Coating for Low NIR Absorption
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Solution Overview
Problem
Dark-color coatings absorb near-infrared radiation, causing substrates to heat up, which is undesirable, especially in applications like motor vehicles, where it increases air-conditioning fuel consumption.
Innovation Solution
A wet-on-wet-on-wet multi-layer coating process using solventborne pigmented coating compositions with specific components like melamine-formaldehyde resin crosslinker, cellulose ester binder, sheet silicate, fumed silica, urea SCA, and polyolefine wax, applied in successive steps with thermal curing, to achieve a dark-color shade with low NIR absorption and heat development.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If dark-color pigments (carbon black) are used in coating, then the coating provides desired dark color shade, but the substrate heats up due to NIR absorption
Solution Approach 1:
The coating is divided into multiple functional layers: a first layer containing IR-reflective pigments (alumina, titania, zirconia) that reflect near-infrared radiation, and a second layer containing dark-color pigments that provide the desired color shade. This segmentation allows each layer to perform its specific function without interfering with the other, solving the contradiction between dark color and NIR reflection.
Solution Approach 2:
The patent uses composite coating structures combining different pigment types in separate layers. The first layer uses inorganic IR-reflective pigments (alumina, titania, zirconia) while the second layer uses organic or inorganic dark-color pigments. This composite approach allows the coating to simultaneously achieve NIR reflection and dark color appearance.
2Temperature
If carbon black pigments are used to achieve dark color, then the coating provides desired color shade, but heat is conducted to the substrate
Solution Approach 1:
The coating is divided into multiple functional layers: a first layer containing IR-reflective pigments (alumina, titania, zirconia) that reflect near-infrared radiation, and a second layer containing dark-color pigments that provide the desired color shade. This segmentation allows each layer to perform its specific function without interfering with the other, solving the contradiction between dark color and NIR reflection.
3Temperature
If light-color coatings are used to reduce heat absorption, then substrate heating is reduced, but the desired dark color shade cannot be achieved
Solution Approach 1:
The coating is divided into multiple functional layers: a first layer containing IR-reflective pigments (alumina, titania, zirconia) that reflect near-infrared radiation, and a second layer containing dark-color pigments that provide the desired color shade. This segmentation allows each layer to perform its specific function without interfering with the other, solving the contradiction between dark color and NIR reflection.
Solution Approach 2:
Different regions of the coating have different optical properties: the first layer is designed to be IR-reflective while the second layer is designed to be dark-colored and NIR-transparent. This local differentiation of optical properties allows the coating as a whole to achieve both NIR reflection and dark color appearance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively produces dark-color multi-layer coatings that minimize heat absorption in sunlight, maintaining a desired color shade while reducing thermal impact on substrates, suitable for industrial mass production.
Implementation Method 1
both coating compositions A and B comprise resin solids consisting of binder solids plus crosslinker solids comprising melamine-formaldehyde resin crosslinker
Implementation Method 2
Dark-color coatings often contain carbon black pigments which absorb radiation in the near-infrared wavelength range and transform it into heat
Implementation Method 3
this occurs via heat conduction, i.e., heat is directly transferred to the substrate from the coating layer containing carbon black pigments and heated by solar radiation
Implementation Method 4
thermally curing the coating layers applied in steps (1), (2), and (4) simultaneously
Data Source
AI summary
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 solventborne coating composition A to a substrate,(2) applying a coating layer B′ from a solventborne coating composition B onto the substrate provided with coating layer A′,(3) subjecting the coated substrate obtained in step (2) to a drying step,(4) applying a clear coat layer, and(5) curing the coating layers simultaneously;wherein both coating compositions A and B comprise binders and crosslinkers comprising melamine-formaldehyde resin crosslinker,wherein both coating compositions A and B comprise certain proportions of cellulose ester binder and NAD binder and/or sheet silicate and/or fumed silica and/or urea SCA and/or polyolefine wax,wherein the pigment content of coating composition A consists 90 to 100 wt. % of aluminum flake pigment and 0 to 10 wt. % of further pigment,wherein the pigment content of coating composition B consists 50 to 100 wt. % of black pigment with low NIR absorption and 0 to 50 wt. % of further pigment.