Roofing granules of enhanced solar reflectance

A method of preparing colored granules comprising the steps of:

• a) crushing and sizing a mineral aggregate;
• b) preheating the crushed and sized aggregate to about 210-230° F.;
• c) coating the preheated granules in one or multiple applications, with a semi-ceramic composition comprising in PPT units:
• 40-60 water
• 55 to 100 sodium silicate solution (SiO2/Na2O=2.8-3.0, % by wt. solids 35.0-40.0)
• 50 to 150 coarse TiO2
• 0 to 50 IR-reflective dark pigments
• 0 to 50 IR-reflective tint pigments
• 20 to 30 Kaolin clay,
• d) combining the components in (c) above with suitable mixing equipment into a coating composition slurry
• e) applying the slurry to the preheated base aggregate to produce uncured color-coated granules
• f) pre-drying the uncured color-coated granules by adjusting the temperature and air flow to reduce their moisture content to about 0.2-0.50%;
• g) kiln-firing the uncured granules at 500° F. to 1000° F. to form an insolubilized silicate-clay matrix in which the IR-reflective pigments and coarse titanium dioxide particles are uniformly distributed;
• h) cooling the fired, color-coated granules by means of air flow and/or water application to reduce their temperature to about 200° F.-220° F.;
• i) optionally repeating steps (c) through (h) to adjust the thickness and composition of the final coating to optimize reflective properties and visual appearance
• j) optionally applying a pickling agent to aid coating insolubilization;
• and
• k) treating the finished granules with a mixture of process oil and an organosilicon compound to impart dust control to improve asphalt adhesion,
• wherein when said colored granules have a Hunter Lightness L>/=25.0, the colored granules have a Total Solar Reflectance of at least 25% and when said colored granules have a Hunter Lightness L<25.0, the colored granules have a Total Solar Reflectance of at least 20%.

Colored granules comprising:

• a) a base material of crushed and sized mineral aggregates in the form of granules;
• and
• b) an insolubilized coating material covering said granules comprising:
• (i) dark IR-reflective pigments;
• and
• (ii) coarse non-pigmentary titanium dioxide of particle size distribution:
• 100% less than 40 microns (−325 mesh)
• 50-100% less than 10 microns
• 0-15% less than 1 micron;
• wherein said coarse, non-pigmentary titanium dioxide is present in amounts of 50 PPT to 150 PPT, for each layer of coating applied.

Colored granules comprising:

• a) a base material of crushed and sized mineral aggregates in the form of granules;
• and
• b) an insolubilized coating material covering said granules comprising:
• (i) dark IR-reflective pigments;
• and
• (ii) coarse non-pigmentary titanium dioxide of particle size distribution:
• 100% less than 40 microns (−325 mesh)
• 50-100% less than 10 microns
• 0-15% less than 1 micron;
• wherein said coarse, non-pigmentary titanium dioxide is present in amounts of 50 PPT to 150 PPT, for each layer of coating applied;
• and
• wherein when said colored granules have a Hunter Lightness L>/=25.0, the colored granules have a Total Solar Reflectance of at least 25% and when said colored granules have a Hunter Lightness L<25.0, the colored granules have a Total Solar Reflectance of at least 20%.