When the hot sun is blazing down which automobile will stay cooler when parked in the open—a white one or a black one? That could be a trick question, but it’s not. White vehicles naturally stay cooler because they reflect about 70 percent of the sun’s heat.
Apart from comfort factors when entering a car on a hot day, the absorption of solar energy puts additional loads on the vehicle’s air conditioner (AC), which impacts fuel economy. According to the US Department of Energy, running a vehicle’s AC in very hot weather can cut fuel economy by anywhere between 5 and 25 percent.
The Impact on Electric Vehicles
The effect of using AC is even more pronounced in electric vehicles, which can decrease driving range by as much as 40 percent. With the global electric vehicle industry continuing to expand rapidly, the need to keep vehicles cooler while relying less on AC will only continue to expand as well.
What if the consumer doesn’t want a white car? Paint formulators have been getting involved over the past few years by developing solar reflective paint for use on cars, trains and other vehicles. The potential benefits are cooler cabins, fuel savings, reduced emissions and extended driving ranges in electric vehicles.
One study appearing in the journal Applied Energy found that a silver car with solar reflective paint reduced that vehicle’s thermal load by up to 11 degrees compared to a comparable black vehicle1. The silver car needed 13 percent less air conditioning to cool the cabin to a baseline 77 degrees.
Automakers typically use carbon black to adjust colors, even in colors beyond straight black. Just a small amount of carbon black can negatively affect solar reflectance because it absorbs sunlight.
Reformulating vehicle coatings, solar reflective paint uses inorganic mixed metal oxide pigment instead of inorganic carbon black, which avoids most of the heat absorption to help mitigate the high temperature issue inside the car.
For reds, blues and other special colors, organic pigments and effect pigments (mica, aluminum) are used to help achieve the desired shade. Specialized titanium oxide grades have been developed to move reflective properties to an improved spectral range, without greatly affecting the color, while also retaining performance properties.
Reconsidering Dispersant Capabilities
However, all these formulating changes mean that a different pigment combination formulation is needed to meet the color specification and additives are needed to avoid rheology or flocculation issues.
Lubrizol offers water-based and solvent-based dispersion technology for a broad range of pigments to disperse small particles in paints and coatings, with different grades available for organic and inorganic pigments. The types of pigments will change for these paints to meet the requirements of solar reflecting properties and to ensure these reformulated paints still meet the same end-point application viscosity.
Lubrizol is working closely with automotive paint suppliers on advancing the solar reflective paint market to balance the need for consumer choice with the need to reflect heat. Contact us to learn more about how we can help you keep your cool in a market that’s quickly heating up.