PURPOSE: To reduce the coating amount of an expensive paint and also the number of processes to lower a production cost, by a method wherein a character, etc. is printed on a printed surface made of a resin material with use of the ink mixed a polyfunctional acrylic ultraviolet-curing paint with a coloring agent, and an ultraviolet light is irradiated onto the printed surface to cure and dry the ink.

CONSTITUTION: A coloring agent is mixed with a polyfunctional acrylic ultraviolet-curing pant to prepare an ink. Using the mixed ink thus obtained, a character 4 is printed on the top surface of a key top 3 made of ABS resin or PBT resin to be of approximately 10μm thick. After the completion of printing, an ultraviolet light is irradiated onto the printed surface of the key top 3 to cure and dry the paint which has been printed in a character or symbol of every sort form. The character which was printed and cured in the above manner is superior in adhesion, release, and wear-resistant characteristics, and have a sufficient resistance to a key-pressing test of ten million strokes.