Color material technology achieving both invisibility and near-infrared absorbability

As one of the ways to reinforce the added value of printing produced by printing presses and printers, Fuji Xerox has studied embedding invisible information on printing materials so that users can read and utilize the information by using such devices as scanners. This technology can be adopted for security purposes, such as creating printed materials embedded with identification information unique to each piece. Also, it might be useful to embed website link information in printing so that users of a particular service can have direct access to a website by using devices equipped with a scanner or network function.
In order to make these ideas a reality, we selected the following items as requirements to find suitable dye materials.

  1. High absorbability of near-infrared light (850 nm: reading wavelength of sensors)
  2. Low absorbability in the visible region, 400 to 700 nm
  3. Lightfastness
  4. A safe chemical material
  5. Relatively low manufacturing cost
  6. Easy-to-handle pigments that enable application to toner or ink

First of all, from a number of candidates, we selected perimidine-based squarylium dyes whose molecule has maximum absorption near 810 nm and almost no absorption in the visible region (Fig. 1). Secondly, in order to satisfy the required performance levels including invisibility and infrared absorption intensity, we introduced various alkyl substituents to the basic structure of this dye molecule and evaluated their performance. As a result, we found that molecular crystallinity was significantly increased with a substituent having a specific sterically branched structure (Fig. 2). This substituent also greatly contributed to improving synthetic yield and lightfastness of the target molecule, in order to create a near-infrared, light-absorbing pigment capable of practical use (Figs. 3 and 4).

This color material technology was adopted for the Fuji Xerox Denshi-Pen Note1 and achieved the output of documents without their high quality images being degraded, even after embedding information throughout the documents. Hereafter, we plan to adapt the technology not only to toner but also to ink and various other printing materials.

  • Note1 This system easily and quickly digitizes handwritten information on existing forms or other documents that customers use at work for a more effective work process.

Fig. 1: Synthesis of perimidine-based squarylium dyes

Fig. 2: Structural drawing of a dye crystal in the A-axis direction

Fig. 3: Absorption spectra of a dye crystal in tetrahydrofuran (THF) solution and solid state

Fig. 4: Reflection spectra allowing for invisible printing
(OK topcoat paper is made by Oji Paper Co., Ltd.)