| 摘要 |
PROBLEM TO BE SOLVED: To improve confidentiality by preventing the output of a paper sheet on which information whose concealing property is lost by a visual color change of toner is recorded. SOLUTION: A white image forming unit 44D for forming an invisible image having the concealing property is adopted as a developing means other than an image unit for forming a visible image. A whiteness level detecting sensor 96 is provided for detecting the visual color change of a white toner image. A white toner patch 116 is created outside the image frame of a photoreceptor belt 12 by the white image forming unit 44D. The whiteness level detecting sensor 96 detects the visual color change of the white toner patch 116. Because the white toner patch 116 is created outside the image frame of the photoreceptor belt 12, it is not transferred on the paper sheet, and does not affect a formed image. |
