| 摘要 |
PROBLEM TO BE SOLVED: To make invisible information readable while limiting a person or a period and to invalidate that at need. SOLUTION: An image forming apparatus includes an image forming unit 41K which forms a K toner image, image forming units 41I<SB>1</SB>, 41I<SB>2</SB>, and 41I<SB>3</SB>which form an invisible toner image, an intermediate transfer belt 46, a secondary transfer device 410, and a fixing device 440. The image forming units 41I<SB>1</SB>, 41I<SB>2</SB>, and 41I<SB>3</SB>form a code image by using toner for invisible information containing near infrared ray absorbers decomposed at different temperatures above 200°C, read code information with a small quantity of near-infrared rays after printing, and invalidate the code information by irradiation with a large quantity of near infrared rays at need. COPYRIGHT: (C)2007,JPO&INPIT
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