• October 23, 2019

The science behind thermal paper

The science behind thermal paper

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Discover just how thermal paper works and the latest developments in creating sustainable solutions for paper receipts.

While receiving receipts for everything we buy is a reassuring – and in some cases, vital – proof of purchase, there aren’t many people that consider just how technologically advanced the equipment is that prints them.

For a start, in the vast majority of tills used around the world, there’s absolutely no ink. The receipts are printed using direct heat transmission, in which tiny heating elements within an electronic till deliver focused heat onto special thermal paper. This paper changes colour when exposed to heat, creating words, numbers, bar codes and even images.

Whether it’s a till receipt for your groceries, self-adhesive labels, parcel labels, lottery tickets, or any piece of paper that needs to be printed clearly, thermal paper is the quickest, quietest and most economical choice.

The science bit

The most common forms of thermal paper use a chemical reaction catalysed by heat to form the colour on the paper. The surface of thermal paper is coated with a dye that can switch between colourless and coloured (a fluoran leuco dye, for example) and an acid. When this mixture is heated above its melting point, the dye shifts to its coloured form, stabilises and a tiny mark is made. Make enough of these marks in the right places and you have a printed receipt.

Since the chemical reaction is contained in the paper and the till equipment simply delivers heat to create the receipt, it’s a relatively simple process with high levels of reliability and no need to add ink. It’s also quick, meaning that the days of waiting while a painfully slow till prints a lengthy supermarket receipt are long gone.

Thermal paper and health

Recently, there have been a number of questions raised about the health concerns of handling paper receipts. Historically, many thermal papers have been coated with bisphenol A (BPA), a chemical which has been banned from some plastic products due to health risks.

However, the European Food Safety Authority and Health Canada consider the presence of BPA in paper receipts to pose no health risk to consumers of any age at current exposure levels.

Whilst exposure to BPA through thermal paper is extremely low, from 1st January 2020, new EU legislation will prohibit BPA being used in the manufacture of thermal paper. In the U.S., producers do not use BPA in the manufacture of receipt paper and the majority of importers do not import paper using BPA coatings.

New products on the market

There are now a number of different receipt papers on the market, including BPA-free thermal paper, which substitutes BPA for bisphenol S (BPS), and phenol-free thermal paper, which uses a colour developer that contains no BPA or BPS in its coatings.

Global paper manufacturer Koehler has also developed a more environmentally friendly thermal paper called Blue4est®, which received the 2017 US EPA Presidential Green Chemistry Award. Blue4est® is a sustainable thermal paper free of chemical developers and can easily be used in any conventional thermal printer. But instead of the dye appearing after being exposed to heat, the emergence of text is a purely physical reaction. It’s safe for direct contact with food and has a 35-year image lifetime.

A sustainable future

The key to the future of thermal paper lies in its sustainability. From a recent global study by Toluna, it’s clear that consumers prefer paper receipts over e-receipts (58% prefer paper, with 64% saying that paper receipts are more practical) and paper is one of the most recycled materials in the world, as well as having a manufacturing industry that prides itself on its low impact on the environment.

With the giant strides being made in developing thermal paper solutions that rely on physical rather than chemical technology, the paper receipt industry will only go from strength to strength.