Infoware NG

As kids we were fascinated by the idea of invisible ink. Writing invisibly with lemon juice and then using the heat of a light bulb to darken the invisible ink and make it readable was a favorite trick. In a sense, what we were doing is creating a primitive version of modern thermal paper.

Thermal paper is the term used for a special paper that has ink already on it, but locked invisibly within a chemical matrix. The matrix breaks down under the application of heat, releasing the ink. Although modern thermal paper has this ink coating over its entire surface, the selective application of heat makes the ink visible only where required to make the desired printing appear.

Thermal paper is most often sold in small roles that fit neatly into the many machines that use them. Things like cash registers, ATMs, and credit card authorization machines all use thermal paper rolls. The tiny rolls usually contain hundreds of feet of paper and the machines use only a few inches at a time as needed to print the receipt or transaction record required, so each roll can last a long time before needing to be replaced.

Like out childhood lemon juice ink, even modern thermal papers only contain a single color of ink and cannot be used for applications requiring multiple colors. That still makes thermal printing very useful for commercial applications where the only thing that needs to be printed is text for things like an automated gas pump receipt.

Another reason why thermal paper is popular for these high volume commercial applications is that thermal printers do not require ink cartridges or printer ribbons. If you have an ink based printer at home, then you know how often ink cartridges and ribbons need to be replaced. In commercial applications, every time the printer requires refilling means down time and can interfere with sales. As those of us with home computer printers also know, replacing ink cartridges can be quite expensive. Thermal printers tend to have a lower operating cost than their ink based counterparts.

Thermal printers also tend to have a simpler design and construction that ink based printers. This makes them cheaper to buy initially and increases their reliability in the long run as well. The fact that they have fewer moving parts than ink based printers means that there are fewer possible points of failure and fewer parts that can wear out over time.

While today’s modern thermal papers are a far cry from the invisible inks we crafted as kids, but they do share enough similarities to bring back some fond childhood memories.