The paper used for the hand-written information input system "Denshi-Pen" is printed with code images that include page IDs for identifying the paper being used and the paper's horizontal and vertical coordinates. The pen used for this technology captures the code images using its built-in, infrared camera and obtains information from the images. Because the black ink of the pen does not absorb infrared light, what is written on the paper does not interfere with the images captured by the camera.
Code images were previously printed with black ink or toner containing carbon black that absorbs not only infrared light but also visible light. However, code images printed in black posed the problem of making the entire paper look gray. To resolve this problem, a high-performance and infrared-absorbing pigment that is almost transparent under visible light was developed to make the code images less visible, as shown in Fig. 1. By adjusting the printing conditions of the dots according to the ink characteristics, the grayness of the paper is rendered unnoticeable, thereby enabling use of the paper for "Denshi-Pen" as if it were regular paper.
Our unique infrared pigment enables both the high absorption of infrared light and transparency in the visible light region (Fig. 2), thanks to molecular design technology nurtured through many years of developing organic semiconductors for our multifunction devices. By introducing a certain substituent with a unique three-dimensional structure for the pigment molecules, the intermolecular force is precisely controlled, ensuring the pigment's resistance to light. This pigment can thus be used in various types of printing material such as ink.
Visible image of code
Infrared image of code
Fig. 1: Images of infrared-absorbing code
Fig. 2: Reflection spectrum of infrared-absorbing ink