Symbol marking tool - applies heated seven-segment resistors to invisible ink spray

摘要

Numbers and other symbols, which can be represented by the possible permutations of a seven-segment display, can be printed on paper or cardboard by a tool which first sprays an invisible ink on the spot. The ink becomes visible only after heating to 200 deg. C. This is done by a seven-segment resistor arrangement in the face of the tool. The segments are arranged by a selector in the combination required to produce the desired marking by heat application. This needs no mechanical adjustment of figure wheels. The preferred ink is a solution of a dye in a mixture of isopropyl alcohol and ethylene monoethylether.