THERMAL COLOR DEVELOPING MATERIAL, THERMAL COLOR DEVELOPING ELEMENT, ITS MANUFACTURE, LAMINATE FOR FORMING THERMAL COLOR DEVELOPING ELEMENT, AND ITS MANUFACTURE

摘要

PROBLEM TO BE SOLVED: To provide a thermal color developing element for irreversibly color developing even in a low temperature range by utilizing a surface plasmon absorption of metal fine particles. SOLUTION: Metal fine particles are generated by a photoreduction of metal ion dispersed in a solid matrix 1 having a melting point in a low temperature range. An aggregation of the particles 2 dispersed in the matrix is suppressed in the state that the matrix 1 is sold. However, when the ambient temperature rises so that the matrix is liquefied, the particles 2 are aggregated to increase its particle size to become particles 12, and exhibit a color developing by a surface plasmon absorption. Since the particles 2 are irreversibly aggregated, even if a temperature drops after the color developing, its color is not erased, thereby visually recognizing its heat history.