What are solar infrared-reflective pigments?
Global Warming and its effect on our planet has become an International issue. We in industry have an opportunity to participate in the reduction of global warming via the application of some of the latest technology to “color” our world in applications such as roofing, sidewalls and other exterior applications.
Researchers in pigment technology have developed a new classification of pigments that are not only extremely durable, weather resistant and color-fast, but also possess a new property – “Solar”, or “Infrared” Reflectivity. This article will discuss this new class of pigments, what they are, the history of the technology, and the features and benefits of their use.
Well, exactly what are Solar Infrared Reflecting Pigments? To answer this we must first examine what Solar Energy is. Solar Energy, or “electromagnetic radiation” from the sun, consists of radiation in the wavelengths from about 250 nanometers (nm) to about 2,500 nanometers.
Ultra Violet – The wavelengths less than 400 nm are referred to as the “Ultraviolet” (UV) region. The UV region contains the shorter wavelengths of radiation that can cause damage to our bodies and also causes much of the photo degradation to paints and polymers.
Visible Light – The range of wavelengths between 400 nm to 700 nm is called the visible region. This region is the area where our eyes are attuned to see light in all its various colors and shades.
Infrared – The final area from 700 nm to about 2500 nm is called the “Infrared” region. These longer infrared wavelengths are invisible to the naked eye, yet contain over half of the solar energy which strikes the earth.
We can see different colors by selective reflection and absorption of various wavelengths in the visible region. We can perceive a color such as a red car, because the radiation (wavelengths of light) in the red portion of the cars pigment (approximately in the range of 650 nm) is reflected back to our eyes, while the rest of the wavelengths (400 to 650 and above 650) are absorbed by the pigment. We can’t see above 700 nm which is the infrared portion of the spectrum, so we really can’t determine what is going on there by sight. However, we can feel the effects of this “Infrared Energy”, in the form of Heat! Touch your asphalt driveway, your conventional asphalt shingled roof, or your black car which has been out in the sun for a while. It’s quite Hot!! In fact some roofing products can reach surface temperatures above 190º F or more. Why is this? It’s because these materials absorb a large portion of the infrared (heat) radiation from the sun.
During the Cold War era scientists began working on pigments which were designed to be spectrally selective for military applications. These pigments were designed to mimic natures’ spectral reflectivity, so that man- made objects could not be observed by sophisticated detection equipment. A good example of this was to spectrally match leaves and trees so that military equipment that was painted with these pigments could not be observed by Infrared detectors while in wooded areas. The first pigments developed for this application were green and matched the spectral curve of the chlorophyll in leaves and grass. It just so happens that leaves and grasses are quite cool to the touch and are actually quite “Solar” or “Infrared” Reflective, thus Solar reflective pigments were born.
The first application of these pigments was for Military Camouflage coatings. It was not until the mid 1980’s that commercial applications were developed out of a need by the vinyl siding industry. It seemed that darker color vinyl siding could not be used commercially because as the temperature of dark colored siding increased, the product sagged on the side of homes. The vinyl siding industry came to Ferro Corporation and asked if they could develop a dark color pigment that could reflect heat and eliminate the distortion problem. Ferro did just that and Infrared Reflective pigments became a commercial success. As technology grew, a palette of colors became available that possessed this High Solar Reflectivity. Today, these same pigments are used in PVDF and Silicone Modified Polyester coatings commonly used for metal roofing applications.
Composition of the Pigments
Just exactly what are these cool pigments and why are they beneficial to industry? These Solar Infrared Pigments are basically synthetic mineral compounds known in the industry as CICP or Complex Inorganic Color Pigments. They are widely accepted as being the best quality pigments available. They are made by reacting mineral compounds together in a calcination process, where these minerals undergo a solid state reaction at temperatures up to 2200º F to make new color compounds. Not all CICP pigments are Solar Reflective however, and only those pigments designated as “Cool” or Reflective, possess the desired properties to reflect the Infrared Solar Radiation desired for today’s applications. Most CICP pigments possess extremely good durability and are well suited for exterior applications. They are widely used in coil coating applications, exterior building products and roofing. These new products are now in great demand and are replacing the currently used CICP products.
The Benefit to Cool Metal Roofing
That being said, why is cool metal roofing so important to industry? First of all, they are able to reflect much of the solar infrared radiation away from surfaces and direct it back out in to space so it does not get absorbed by the roofs and other applications where it is used. A typical black pigment such as carbon black, will reflect only about 3-4% of the total solar energy that strikes the surface. This means it absorbs about 96% of the solar energy which shines upon it and gets very hot!! In contrast a “Cool” black pigment in very dark color space can reflect about 25% of the Solar radiation and thereby remain cooler. How much cooler will the cool metal roof with these pigmented paint systems be? Theoretically, for every 1% (0.01) increase in a roof’s reflectivity the surface temperature could be 0.75ºF cooler, or for very 10% more reflective a roof surface is, it could be up to 7.5ºF cooler