Multi-layer Coating Process for NIR Heat Reduction
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Solution Overview
Problem
Dark-color coatings containing carbon black pigments 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 multi-layer coating process involving an NIR-opaque coating layer with 90-100% aluminum flake pigment and a waterborne pigmented coating composition, followed by a coating layer with 50-100% black pigment, both containing aqueous microgel and sheet silicate, applied wet-on-wet-on-wet and simultaneously cured, to minimize heat absorption and maintain desired dark-color shade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If carbon black pigments are used in dark-color coatings, then the coating achieves desired dark-color appearance, but the substrate heats up due to NIR absorption
Solution Approach 1:
The coating is divided into multiple functional layers: an NIR-reflective base layer (containing aluminum flake pigments) and a dark-color top layer (containing carbon black pigments). This segmentation allows each layer to perform its specific function - the base layer reflects NIR radiation while the top layer provides the desired dark appearance, resolving the contradiction between heat absorption and color appearance.
Solution Approach 2:
The invention uses composite coating compositions combining different pigment types (aluminum flake pigments with specific thickness ranges of 10-80 nm or 80-200 nm) and binder systems (waterborne acrylic resins with specific glass transition temperatures). This composite approach enables simultaneous achievement of NIR reflection properties and dark-color appearance.
2Loss of energy
If aluminum flake pigments with thickness 10-80 nm are used, then NIR reflection is improved, but coating composition complexity increases
Solution Approach 1:
The invention specifies precise parameter ranges for aluminum flake pigment thickness (10-80 nm or 80-200 nm) and binder glass transition temperature (50-150°C) to optimize NIR reflection while maintaining practical manufacturability. These parameter specifications balance performance requirements with manufacturing feasibility.
3Productivity
If wet-on-wet-on-wet coating process is used, then production efficiency is improved, but coating quality control becomes more difficult
Solution Approach 1:
The coating compositions are pre-formulated with specific properties (NIR-reflective base layer composition, dark-color top layer composition with controlled pigment content) to ensure proper layer formation and separation during the rapid wet-on-wet-on-wet application process. This preliminary preparation enables high-speed production while maintaining coating quality.
Solution Approach 2:
The invention uses a clear coat layer as an intermediary between the base layer and top layer, and also employs binder systems with specific glass transition temperatures as mediators to control layer interaction and separation. These intermediary elements facilitate the wet-on-wet-on-wet process while ensuring proper layer differentiation and quality.
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 reduces heat development in sunlight while maintaining a dark-color appearance, suitable for industrial mass production, even with short time intervals between coating steps, thereby optimizing energy efficiency and color retention.
Implementation Method 1
aluminum flake pigments which are 10 to 80 nm thick... NIR-opaque coating layer exhibits low NIR absorption
Implementation Method 2
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
Implementation Method 4
both coating compositions A and B comprise aqueous microgel and sheet silicate... prevents intermixing of the coating compositions once applied to a substrate
Implementation Method 5
the combination of aqueous microgel and sheet silicate in each of the coating compositions A and B prevents intermixing of the coating compositions
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 waterborne pigmented coating composition A to a substrate, (2) applying a coating layer B' from a waterborne pigmented 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 aqueous microgel and sheet silicate, 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.