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IR pigments reflect solar radiation and keep polymer products cooler

IR pigments reflect solar radiation and keep polymer products cooler

26-Feb-10
In the hot summer, when a car is parked without shade, the black instrument panel, seats and steering wheel grow unbearably hot, as also dark surfaces of building roofs and fa�ades. Dark surfaces heat up more than light surfaces because they absorb the incident sunlight and convert it into heat, while light surfaces reflect most of the incoming energy. All light, whether visible or invisible, will heat an object that absorbs it. The more solar energy an object absorbs, the greater will be the heat build-up, while the more reflective an object, the less it will heat when exposed to sunlight. Infrared (IR) is largely responsible for heat build-up. Ultraviolet light and infrared light are invisible to the human eye and have no affect on color. Two objects can be identical in visible color yet have different reflective characteristics in the IR region so that one remains cooler on exposure to sunlight. Pigments provide color by absorbing and reflecting different parts of the sun�s wavelength spectrum based on their chemistry. Color pigments selectively absorb visible light, and what light it reflects appears to the human eye as color. While nearly 40% of the sun�s energy occurs in the visible light range (400-700 nm), more than 50% of the sun�s energy is in the non-visible infrared region (700-2500nm).
Pigments can be specifically formulated to have high IR reflectivity to counteract solar heat buildup. Reflecting pigments have been designed to reflect infrared light while still absorbing the same amount of visible light. If the pigment has low infrared absorption, then it is �cool�, while a pigment with high infrared absorption is �hot�. Cool pigments can be used as a colorant compounded into polymer to counteract solar heat buildup. This ability to stay cool even under very intense sun offers a range of benefits as they provide a longer life to the polymer product. Cool products retain color, gloss, flexibility and mechanical properties. Cool products last longer. IR-reflective pigments come in a wide range of colors that prevent solar heat build-up regardless of tone or shade. The pigments� special reflective properties mean that they simply bounce back the infrared rays, and thus the heat of the sun or any other heat sources. IR-reflective pigments also prevent surface deterioration, delamination, warping, distortion and other types of degradation and failure that accumulated heat can cause. The pigments can be used with many different polymer resins and production processes. IR Reflection keeps the polymer surface cooler. Heat destroys material properties so cooler materials retain material properties better. Thermal expansion and contraction leads to warping, distortion and even part failure, and reducing the temperature swing reduces these problems. Prolonged heat degrades polymers, so reducing the heat helps to improve longevity.
Although these physical principles at first appear unalterable, innovative pigments from BASF make it possible for surfaces to heat up much less in the sun despite their dark color: Paliogen Black, Lumogen Black and Sicopal Black. In contrast to carbon black, the standard black pigments, they reflect most of the invisible near infrared (NIR) radiation which accounts for more than 50% of the total incident solar energy. Because they swallow up the visible light completely like any conventional black pigment, the optical impression of blackness is preserved. In this way Paliogen Black and Lumogen Black reflect up to 45% and Sicopal Black up to 30% of the total incident solar radiation energy. By comparison: for carbon black, the total solar reflectance (TSR) is less than 5%. In practical trials, the lower NIR absorption compared to other black pigments results in a temperature decrease of up to 20 degrees Celsius on the surface, inflicting less strain on the material. They benefit not only as pigments in purely black surfaces: paints, coatings and plastics in almost all other color shades also contain greater or lesser amounts of black pigments. If the BASF black pigments are used instead of carbon black, these colors also heat up much less in the sun. However, they exert this effect in different ways: Paliogen Black and Lumogen Black from the class of organic pigments, initially allow the NIR radiation to pass almost unhindered. What happens to it then depends on whether the substrate reflects or absorbs radiation. In addition to their NIR properties Lumogen black pigments have good temperature stability as well as great resistance to chemical and physical effects making them useful for plastic paneling, rigid PVC window frames and the interior trim of vehicles. Sicopal Black K 0095, on the other hand, reflects the NIR radiation on its own and thus functions independently of the substrate � although the effect can be further optimized by a reflective substrate. The inorganic pigment is particularly weather, temperature and chemical resistant. The NIR-reflecting black pigment, Sicopal Black K 0095, finds application in coatings and plastics. This pigment allows a significant reduction in the solar heating of dark black structural components for the building and automotive industries. Sicopal Black K 0095 combines excellent reflection values in the near infrared with the most intense, neutral black shade on the market, making it possible to mix neutral gray shades in all degrees of lightness. With its extremely high heat stability typical of inorganic pigments as well as high resistance to migration, it is resistant to chemical and physical attack making it suitable for a wide range of demanding applications, such as mass-colored building components, roof shingles, and roof film systems and slate-gray polyolefin elements.
A new black pigment Black 40P925 introduced by Shepherd Color Company, designed specifically for coloring fibers, films, and molded/extruded parts. Black 40P925 is also part of the Arctic range and can be used to minimize heat build up and reduce overall energy costs. Shepherd�s Arctic� pigments reflect the infrared portion of the Sun�s light. Because IR light contributes greatly towards heat build up, items made with Arctic� pigments reduce the temperature of products that are exposed to the sun without sacrificing color. This can extend product life, cool interior spaces or contents, retard degradation, or mimic the spectral properties of foliage for military camouflage. Arctic Infrared Reflective Pigments mitigate solar-induced heat build-up and the destructive events associated with it. These pigments are an excellent choice for outdoor applications. Fiber uses include; awnings, tents, carpeting, and furniture textiles. Uses for outdoor opaque thin films include; profiles, windows, doors, siding, marine docks and agricultural films.
They are 100% high performance inorganic pigments. Their characteristics include extreme durability, outstanding high temperature stability; they are chemically inert, insoluble and resistant to bleeding and migration, as well as being lightfast, and weathering well. Compared with standard pigments, they have exceptionally low extruder pressure build up. PRECISE pigments are engineered to have excellent dimensional control to enhance your productivity. They pigments are also useful for coloring high temperature, engineered resins with use in fibers and thin films. Inorganic oxides, in particular, high performance inorganic pigments formed through high temperature (>800� C) solid state reactions, provide heat stable solutions.
IR pigments find application in vinyl siding, lawn furniture, pickup truck beds, car exteriors and interiors; t-shirts and children�s play equipment. Certain plastics such as polyesters are particularly sensitive to solar heat buildup and will lose physical properties in addition to gloss and color. Stresses caused by expansion and contraction of plastic through solar heating cycles can loosen fasteners and cause temperature sensitive products such as rigid PVC for vinyl siding and window/door profile applications to warp or twist out of shape. Dark surfaces subject to solar heat buildup in car interiors and composite decking can also cause significant user discomfort. A cool roof in general reduces urban temperatures and more specifically decreases a building's cooling load. By using IR reflective pigments it is possible to formulate materials that look like foliage both to the human eye and infrared imaging equipment.
The demand for NIR-reflecting black pigments for paints and coatings is constantly growing. There are many applications for these �cool paints�, ranging from roofs through facades to metal containers for international shipping traffic to protect their contents against the searing tropical sun. And their use is not restricted to coatings, because the pigments are also suitable for coloring plastics. As representatives of the organic pigments, the Lumogen Black range of pigments are recommended for use in plastics because of their greater temperature stability. This opens up many possibilities for plastic paneling, window frames and not least, the entire interior trim of vehicles.
 
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