Scientists hope to commercialise rewritable paper

Jo Francis
Monday, February 13, 2017

Scientists in the US have developed a light-printable, ink-free rewritable paper that uses nano technology.

The Yin Group at the University of California, Riverside, Department of Chemistry is led by Professor Yadong Yin, and specialises in the “synthesis and functionalisation of nanostructured materials”.

Yin’s team has published a research paper detailing their latest findings in the field of high-performance light-printable rewritable paper.

The researchers have developed a new photoreversible colour switching system (PCSS) using Prussian blue dye integrated with titanium oxide nanoparticles, which they claim can be easily applied to the surface of conventional paper. The paper is imaged using UV light, which causes electrons from the titanium oxide to move to the dye in the nanoparticle.

Prussian blue dye results in either white words on a blue background, or blue words on a white background. Other colours have also been tested.

The rewriting performance is described as “outstanding” at up to 80 times. The image lasts for up to five days, and can be erased by heating at 120-150°C.

Yin told PrintWeek: “We believe the rewritable paper has many practical applications involving temporary information recording and reading, such as newspapers, magazines, posters, notepads, writing easels, product life indicators, oxygen sensors, and various rewritable labels.”

The potential benefits claimed included forest conservation, pollution reduction and resource sustainability.

The research has been underway for a number of years, and a short YouTube video (see below) shows an earlier rewritable substrate being imaged using a mask. The group’s previous colour switching system used organic dyes, which could only be applied to nonporous substrates such as glass and plastic sheets.

Chemists at the University of California, Riverside fabricate novel rewritable paper

However, the current method can be applied to conventional paper, and Yin said it was now possible to ‘print’ directly using light. “We have actually developed a light printer and used it for printing images already,” he explained.

He said the opacity of the paper would depend on the concentration of the dye or pigment (in this case Prussian blue), or the thickness of the film. “We can easily increase the opacity to the same level as the regular prints from laser or inkjet printers,” he stated.

“The resolution can be very high. Small features down to 10 micrometers can be printed. As our focus has been mainly on the materials development, and we mostly used masks for printing, we haven't fully demonstrated the printing details such as tints and halftones. But we believe these should be rather easy to achieve when we use light for direct printing,” Yin added.

Yin said that the process of commercialising the technology was underway. “If everything goes well, we should expect products on market within two years.”

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