How Ink-free Mobile Photo Printers Work

Ink-free Mobile Photo Printer Paper: The Magic Behind Portable Photo Printers
These microscopic crystals are the only "ink" that Zink paper needs.
These microscopic crystals are the only "ink" that Zink paper needs.
Zink Imaging

So how do you print a quality photo by installing just paper and absolutely no ink? It's no magic trick -- the answer lies in the paper itself. Observe: before printing, the blank Zink paper is white and seemingly normal. However, like the saying goes, it's what's inside that matters.

Scientists at Zink invented a paper that contains all the "ink" necessary to make a photo. Each sheet of the Zink paper contains dye crystals: some that can turn cyan, some that can turn magenta, and some that can turn yellow. These crystals are imperceptible to the naked eye and, before printing, are colorless. To activate this untapped, imperceptible "ink" in the crystals, add heat to the equation. Heat causes a chemical reaction in these specially designed crystals, turning them from colorless crystals to richly colored dye.

To get a closer look at how the paper works, let's inspect the different layers:

  1. Base layer: This first layer provides the paper template on which to place layers of crystals. This layer can also have an adhesive back, as with the Polaroid PoGo instant mobile printer.
  2. Cyan imaging layer: an image-forming layer that releases a cyan-colored dye when activated at a lower temperature for a long time.
  3. Magenta imaging layer: the layer that releases magenta dye when activated at a medium temperature for a medium amount of time.
  4. Yellow imaging layer: This layer releases yellow dye when activated at a high temperature for a short amount of time.
  5. Overcoat layer: Last, but not least, is this protective layer of clear polymer that seals the paper, which allows it to resist damage from light, heat and water. This layer lends the photo a traditional glossy feel.
In Zink paper, the "ink" is embedded in three layers of heat-reactive dye crystals, sandwiched between a base and protective overcoat layer.
Zink Imaging

Also, interlayers in between the imaging layers listed above keep the imaging layers separate from each other. 

As the paper goes through the thermal printhead, the color activated depends on the printhead's temperature and time of application. For example, if the printer needs to activate magenta alone, the heat applied will not be hot enough to activate yellow crystals and won't be applied long enough to activate cyan crystals.

Here, a pile of unrefined dye crystals sits on a pool of activated magenta dye.
Zink Imaging

The "lower" temperatures and "longer" amounts of time used on these printers are really neither low nor long -- temperatures are hot, ranging from 212 to 392 degrees Fahrenheit (100 to 200 degrees Celsius), and printing one line takes only 16 milliseconds [source: Clarence].

Different mixtures of cyan, magenta and yellow can yield all the colors that you need to print a quality image. Each 2-inch by 3-inch sheet contains about 100 billion dye crystals and gets activated by 200 million heat pulses [source: Zink].

Although years of toil went into perfecting the science of this paper, Zink has managed to produce it cheaply enough to sell it for about $3 per 10-pack (about 33 cents per sheet) for the PoGo printer [source: Kirsner]. And, although Polaroid's PoGo printer uses 2-inch by 3-inch paper, Zink can produce paper of any size. As Zink and its other partnering companies develop other compatible printers, more sizes will be available.

So, we know this printer is compact and mess-free, but does it have any drawbacks? What are its strengths and weaknesses? Read the next page to learn more.