Method for reading of invisible marking

摘要

The present invention provides a method for reading of information, which comprises printing information on a metal substrate or a substrate capable of transmitting infrared rays of 2-10 mu m wavelength, with a marking ink containing tin oxide, indium-tin mixed oxide, or a mixture of tin oxide or indium-tin mixed oxide and at least one compound selected from the group consisting of alumina, barium sulfate, silicon dioxide and calcium carbonate, as necessary coating a clear coating or a coloring ink on at least the information-printed area of the substrate, and identifying the information by the use of a CCD camera sensitive to infrared rays of 2-10 mu m wavelength or an infrared detector. According to the present method, no noise is generated even when the reflectance of a light from the substrate surface is large, and the information can be identified (read) easily.