‘Shrinky Dinks’ Manufacturing Process Developed

NC State demo of new infrared light-triggered process to assemble 3D objects out of 2D paper.
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TINA CASEY

The development of ultra-fast, ultra-cheap manufacturing technologies has become a national priority, so much so that DARPA, the Defense Department’s premier advanced research agency, has put out the call for innovators to come up a whole new approach to getting stuff off the drawing board and into action as quickly as possible. Scientists at North Carolina State University have devised a light-based 3D assembly process seemingly based on Shrinky Dinks, the popular children’s craft toy.

The researchers have created flat forms of shape memory polymers that quickly assemble themselves into three-dimensional shapes, simply by exposing them the infrared light of a heat lamp. The team described the results in a paper published in the journal Soft Matter.

One example of the team’s work is a small box with a lid that snaps into shape all by itself within seconds. Visually, it looks like an invisible person is folding an origami box at fast-forward speed.

Like Shrinky Dinks, shape memory polymers are plastics that change their shape when a trigger is applied, such as light or heat.

If you don’t know your Shrinky Dinks (maybe you weren’t alive during or slept through the ’80’s?), the toy consists of thin pieces of clear, flexible plastic, precut into shapes or sold in whole sheets, that you color and bake in the oven. The heat induces shrinkage with minimal distortion of the original shape, and the end result is a smaller, thicker, brightly colored rigid plastic object.

To achieve that property, North Carolina State researchers used a conventional inkjet printer to imprint thin black lines onto sheets of memory plastic. Under the infrared light, the black lines absorbed more energy than the rest of the sheet, causing only the plastic below them to contract. In effect, the printed lines act like hinges on springs that are activated by light.

This light-sensitive process has a clear cost advantage over other shape memory polymer research, which typically relies on developing new plastics with different chemical properties.

“This is a novel application of existing materials, and has potential for rapid, high-volume manufacturing processes or packaging applications,” explained research team member Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NCSU in a statement for the press.

The self-assembling concept is a significant step forward for a number of reasons. The most straightforward advantage is its potential for use in manufacturing processes that can operate at higher speeds while using far less energy than conventional molding or mechanical folding.

A secondary benefit — and one of particular interest to the U.S. military — is the potential for domestic self-assembly plants to churn out spare parts and other essential equipment quickly and cheaply within U.S. borders, reducing reliance on foreign suppliers.

The relatively large-scale processes envisioned by Dr. Dickey are just one potential application for printable memory plastics. At the other end of the size spectrum, the print-and-shrink concept is also under development by researcher Michelle Khine of the University of California in two other significant tech areas, microfluidics and solar power.

Khine first turned to Shrinky Dinks as the only way she could afford to design and fabricate miniature diagnostic devices known as “labs-on-a-chip.” She found that a pattern printed on Shrinky-Dink plastic would create perfect micro-scale channels, as shrinkage causes the inked lines to form tiny ridges.

Khine is currently applying the same print-and-shrink principle to develop low-cost photovoltaic cells through a subsidiary of the company she co-founded, named (take a wild guess) Shrink Nanotechnologies.

In an art imitates life twist, Shrinky Dinks is also encouraging its customers to exploit the mass production potential of its product by using common inkjet printers and copiers rather than hand-coloring. The company even sells plastic sheets especially designed for machine use, though it warns customers to use inkjet only; laser would melt the plastic.

Inspired? If you just bought strawberries in a clear plastic tub, check the bottom for the recycling number. If it says #6, that’s essentially the Shrinky Dink shape memory polymer, and that’s all you need to start your own manufacturing revolution.

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