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Leuco dyes change color over a broader temperature range and are available in a wider range of colors. “A gamut of colorants is available that will make a transition through a broad set of temperature ranges from –25ºC to +65ºC. Leuco dyes are the primary colorants used in packaging inks,” he says.

Chuck Boyce, managing director, Matsui International Co., Inc., explains that Matsui’s Chromicolor® product consists of three major components enclosed in a microcapsule: leuco dye, color developer, and a solvent. “When the solvent is at a high temperature, it is a liquid, which causes the dye and the color developer to come apart,” he says. “When the solvent solidifies, the dye and the developer combine to form a color. Different color change points are achieved by the use of different solvents. These microcapsules can then be used to create inks, paints, and plastics that can react at different temperatures to change color.”