Optical Thread Thwarts Designer Knockoffs

A thread with optical properties can be used to create invisible patterns in fabric and is seen as a potential way to differentiate designer clothing from knockoffs.

Trade in counterfeit and pirated goods has exploded in the past few years, not only in Sweden but also in the EU and globally, according to Swedish customs. One reason is that it can be difficult to tell the difference between a genuine garment and a fake.

Using invisible thread can help clothing manufacturers create a logotype that is part of the actual fabric and that becomes visible only under polarized light. The technology produces a specific optical spectrum that is very difficult for pirate manufacturers to copy. Courtesy of Christian Müller.

As a potential solution, Chalmers University of Technology polymer technology researcher Christian Müller created a partially invisible thread made of polyethylene and a dye molecule that absorbs visible light. The thread can be woven into a pattern that is invisible to the naked eye but that can be revealed using a polarization filter.

"The production process itself uncomplicated," he said. "Clothing manufacturers could start using the thread right away to put a signature pattern in their garments. The equipment needed to see the pattern is fairly simple and is already in place at Swedish customs, for example."

A similar technology is also being used in Switzerland for creating invisible patterns on currency to prevent counterfeiting.

The invisible thread can be created using several different dye molecules and several different synthetic fiber textiles such as nylon. The dye molecule can also be bonded to natural fibers such as wool and silk. The technology can be used both for clothes and for different types of expensive specialty fabrics, such as those used in vehicles.

The idea is for a brand to be associated with its own special combination of textile fibers and dye molecules. The thread is easy and inexpensive to produce.

"It is very difficult for pirate manufacturers to copy the unique combination," Müller said. "They can obtain the equipment needed to read the pattern and ascertain the optical spectrum produced by a specific signature, but they cannot know which combination of components will produce the specific spectrum. And there are loads of different dye molecules available for use."

In the future, the technique also could be used to manufacture "smart textiles," such as clothing that changes color based on electrical charge.

The results were published in Applied Physics Letters in 2012 (http://dx.doi.org/10.1063/1.4764518).

For more information, visit: www.chalmers.se/en/