Multi-layer Composite Coating for Low NIR Absorption
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Solution Overview
Problem
Dark-color coatings containing carbon black pigments absorb near-infrared radiation, causing substrates to heat up through heat conduction, which is undesirable for the substrate material and its interior.
Innovation Solution
A multi-layer composite is created using a transparent plastic film with a multi-layer coating on its back face, comprising a pigmented coating layer A′ with 50-100% black pigment for low NIR absorption and an NIR-opaque coating layer B′ with 90-100% aluminum flake pigment, applied in successive steps to minimize NIR absorption and maintain a dark color with minimal brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a dark-color coating containing carbon black pigment is applied to provide a dark color surface, then the brightness L* is reduced to at most 10 units, but the substrate heats up due to NIR absorption and heat conduction
Solution Approach 1:
The coating is divided into multiple layers with different functions: a first coating layer (A') containing black pigment with low NIR absorption for dark color appearance, and a second coating layer (B') containing aluminum flake pigment for NIR reflection. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between dark color and low temperature.
Solution Approach 2:
The invention uses a composite multi-layer coating structure combining different pigment types (black pigment with low NIR absorption and aluminum flake pigment) in specific layers. This composite approach creates a coating system that simultaneously achieves dark color appearance (brightness L* ≤ 10) and low substrate temperature by reflecting NIR radiation, thus resolving the technical contradiction.
2Illumination intensity
If carbon black pigment is used to achieve dark color appearance, then the brightness L* is reduced, but the pigment absorbs NIR radiation and transforms it into heat
Solution Approach 1:
The invention converts the harmful NIR absorption property into a beneficial reflection property by using aluminum flake pigment in the second coating layer. The aluminum flake pigment reflects NIR radiation that would otherwise be absorbed and converted to heat, while the first layer with black pigment maintains the dark color appearance. This transforms the energy loss into energy reflection, resolving the contradiction.
Solution Approach 2:
Different layers of the coating have different local qualities: the first layer (A') contains black pigment optimized for dark color appearance with low NIR absorption, while the second layer (B') contains aluminum flake pigment optimized for NIR reflection. This local differentiation allows each layer to perform its specific function, resolving the contradiction between dark color and NIR energy management.
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 multi-layer composite effectively reduces substrate heating in sunlight, providing a dark-color surface with minimal temperature increase, suitable for decorative and protective applications on various substrates.
Implementation Method 1
an NIR-opaque coating layer B′ from a pigmented coating composition B onto the coating layer A′, wherein the pigment content of coating composition B is either a pigment content PC1 consisting 90 to 100 wt. % of at least one aluminum flake pigment
Implementation Method 2
the pigment content of coating composition A consists 50 to 100 wt. % (weight-%) of at least one black pigment with low NIR absorption
Data Source
AI summary
A process for the production of a multi-layer composite comprising applying a coating layer from a pigmented coating composition A onto the back face of a transparent plastic film and then applying an NIR-opaque coating layer from a pigmented coating composition B, wherein the pigment content of coating composition A consists 50 to 100 wt. % of black pigment with low NIR absorption and 0 to 50 wt. % of further pigment, which is selected in such a way that coating layer A′ exhibits low NIR absorption and that the multi-layer composite exhibits a brightness L* of at most 10 units, wherein the pigment content of coating composition B is either a pigment content PC1 consisting 90 to 100 wt. % of aluminum flake pigment and 0 to 10 wt. % of further pigment, which is selected in such a way that NIR-opaque coating layer B′ exhibits low NIR absorption, or a pigment content PC2 comprising <90 wt. % of aluminum flake pigments and being composed in such a way that NIR-opaque coating layer B′ exhibits low NIR absorption, and wherein coating layers A′ and B′ are cured.