Thermal transfer sheet, printing sheet, and thermal transfer printing apparatus

A thermal transfer printing apparatus including a thermal head and a platen roll and in which the thermal head heats a thermal transfer sheet including a dye layer and a protective layer containing an invisible light absorbing material to transfer a dye onto a printing paper while the thermal transfer sheet and the printing paper, lying one on the other, are transported between the thermal head and the platen roll, thus forming an image on the printing paper and transferring the protective layer onto the image, the thermal transfer printing apparatus comprising:

• a detector disposed between a feeder feeding the thermal transfer sheet and the thermal head, the detector applying invisible light to the protective layer and measuring an intensity of invisible light transmitted through or reflected from the protective layer;
• a memory storing a table in which a type of the thermal transfer sheet and the intensity are associated with each other;
• and
• an identification referring to the table and identifying the thermal transfer sheet fed from the feeder based on a measurement result of the detector.

A printing sheet comprising:

• a substrate;
• an intermediate layer disposed on the substrate;
• and
• a receiving layer disposed on the intermediate layer,
• wherein the intermediate layer contains an invisible light absorbing material and is provided with an identification mark including at least one of a recessed portion and a protruding portion.