IR reflecting pigments

Metallic pigments reflect infrared radiation and hence are able to reduce the heat emission from a surface coated therewith, according to Kirchhoff s law 1-/J(A.) = e(X,), where R = reflectance and e = emissivity. Hybrid polymers are superior to commercially available binders, considering both miscibility with IR-reflective pigments and the achievable degree of filling. However, in order not to affect the optical function of the pigments, the infrared absorption of the binder should also be as... 

Colorists, when choosing pigments for a formulation must optimize cost and performance, often a complex task. Formulation with IR reflecting pigments adds constraints in selecting and formulating. We wiU be discussing these additional concerns. 

Figure 25. Dependence of the reflectance of chromium oxide on the wavelength a) Regular pigment b) Special product with larger particle size and high IR reflectance...

From an application standpoint, high opacity, heat stability, IR reflectance, Hght-and weatherfastness as well as chemical resistance are the main reasons for using these pigments. Recent developments focus primarily on more economic higher strength versions, but there is also mention of new chemistries like Zn/Sn rutiles [3.85], new IR reflective chemistries [3.86, 3.87] as well as mixed metal oxides for new application fields Hke laser marking [3.88]. 

By incorporation of infrared (IR)-reflective metallic pigments into masonry paints, the heat emission from buildings can be efficiently reduced [1]. As a result the wall will cool down less at night, which prevents the formation of dew on the surface. Thus, corrosion by humidity is minimized as well as soiling due to humidity-induced growth of microorganisms. 

This paper describes the synthesis of the novel hybrid binders and demonstrates their usefulness with respect to incorporation of IR-reflective metallic pigments. 

Cerium sulfide pigments are also good candidates for automotive paints, due to the IR reflectance properties of Cerium compounds (Figure 4—15). 

The mixed chromite/ferrite spinels, C.I. Pigments Brown 33 and Brown 35, provide darker browns than the pure ferrites, covering the color range from reddish-brown to nearly black. These products are used mainly in plastics and coatings to provide heat stable colors. In addition. Brown 35 spinels have good IR-reflective properties, and are used in low heat build-up plastics and coatings. 

The great feature of these pigments is their good IR reflectivity. They generally have higher IR reflectivity than other dark IR-reflective CICPs, as demonstrated in Figure 5-5. These browns and blacks are primarily used to prepare dark exterior durable colors with low heat build-up. 

Figure 6-5 shows UV-Vis-NIR reflectance spectra of some DR pigments. The DR pigments exhibit good UV absorbance and high IR reflectance - properties that enhance their performance in outdoor weathering systems. 

Figure 5.5 Reflectance spectra of two IR-reflective CICPs compared with a non-reflective Pigment Black 28. Dips in reflection centered at 1700 and 2300 nm are due to the polymer matrix.

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