Ink Treatment Enables Desktop Laser-Based Paper Cutting
Olivier Acher sympathizes with anyone who has struggled to get business cards or invitations printed on short notice. These and similar tasks depend on the availability of paper that has been precut or scored into standard shapes and sizes.
Acher, chief scientist and deputy manager of the materials department at the Commissariat à l'Energie Atomique Le Ripault in Monts, France, knows that businesses are built upon supplying such precut paper, but he also understands that fitting into someone else's predefined format is not easy.
Office paper has a low absorptance at wavelengths accessible using commercial high-power laser diodes (top). The application of black or near-IR ink, however, makes it possible to cut, score or produce fold lines in paper using a 1-W near-IR laser diode (bottom).
"It is not convenient," he said, "because, as a rule, you always miss the proper precut format you want to use."
Acher and his group at the agency have demonstrated a paper-cutting technique based on infrared laser diodes and black or near-IR-absorbing ink. Their method could be incorporated into desktop ink-jet printers, enabling paper to be cut or scored on demand into desired shapes and three-dimensional structures.
"Our technology is a smooth step from desktop printing into personal fabrication," he said.
Existing laser-based paper-cutting systems use kilowatt-class CO2 lasers to cut at speeds of hundreds or several thousand meters per second, but they are too expensive for desktop use. Relatively inexpensive laser diodes can now pump out 1 W at wavelengths greater than 700 nm, so the group decided to investigate their suitability in this application.
Depending on the speed of the laser across the paper, the system cuts (top) or scores tear lines (bottom).
Standard office paper absorbs less than 5 percent of the incident radiation at wavelengths between 450 and 1400 nm, so there is insufficient interaction for a 1-W laser diode to produce a cut. The researchers therefore looked at the effect on the absorptance of black ink from a common marker and of an "invisible ink" that they formulated using an IR-absorbing pigment from Sigma-Aldrich Co. of St. Louis. They found that paper marked with the black ink had an absorptance of more than 90 percent at 820 nm, and that paper marked with the invisible ink had an absorptance of 80 percent.
In the prototype paper-cutting system, they used a 1-W single emitter with a peak at 810 nm. Acher, who has used laser diodes from multiple sources, said that the important device parameters are sufficient power at the right wavelength and for the right price.
In tests of the approach, the researchers marked lines on paper with the inks and mounted the samples onto a rotating, high-thermal-conductivity drum. They used a focused beam from the laser diode to cut the paper, varying the laser's power, the drum's speed of rotation and the type of ink. The tests revealed that both the black marker and the near-IR ink worked well. The cutting speed was approximately 1 m/min with the black ink.
They also found that their technique could create tear and fold lines. At speeds up to 20 percent faster than those that resulted in a cut, they scored tear lines. The perforations might be used in a tear-off coupon. At speeds 20 to 100 percent faster than those yielding a cut, they produced fold lines, which would make it easy to create the bend points needed for a stand or another three-dimensional structure.
Integrating such a paper-cutting system into an ink-jet printer would require the addition of a laser diode; an ink reservoir to mark the cuts, scores or folds; some additional optics; and a high thermal conductivity drum. A 1-W laser diode would enable cutting speeds of several pages per minute for most applications, and its added cost is estimated at approximately $20 for high-volume production. The optics to focus the beam's spot size down to around 50 µm and the high thermal conductivity drum also would add a negligible expense.
Acher and the research agency's marketing bureau think that such a system could be successful, and there is an effort in the works to commercialize the technology. He believes that there is a basic, visceral reason why laser paper fabrication will flourish: "Paper is not just a display, but also something you can fold, put in your wallet and hand to another person."
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