Feasibility study of thermochromic inks for the packaging industry

Abstract

A thermochromic ink is defined as an ink that exhibits colour changes depending on temperature.
Thermochromic inks used in printing generally consist of an encapsulated three part system which includes a dye that changes colour, a compound that acts as a colour developer and a solvent. Due to the properties of the dye, the inks are always colourless above a certain temperature and coloured below a certain temperature. This study seeks to investigate the feasibility of using
thermochromic inks in the existing packaging manufacturing process at Tetra Pak. Inks that have these properties could be relevant for companies in the packaging industry to create smart packaging materials to differentiate products. To analyse the properties of thermochromic inks,suitable thermochromic inks for water based flexographic printing were ordered from two different ink suppliers along with printed samples from a third ink supplier. By using L*a*b* measurements and calculated ΔE## values, different flexographic printing parameters including anilox volume and substrate were tested in lab scale tests. The measurements were carried out at different temperatures to analyze the colour changes in detail. After the lab tests, pilot tests were carried out to verify if the process behaves accordingly at a greater scale. The results from the
pilot tests corresponded well with the lab results. When testing high temperature stability it was found that high temperatures, above 300 °C that is prevalent during lamination, did not have an impact on any of the inks tested in this study. It was observed that for all inks tested in this study the ink layer is visible at room temperature and not transparent to the paper surface. The inks
tested in this study follows major food safety regulations but the next step would be to perform internal migration tests at Tetra Pak.

Popular Abstract

Smart labels on food packages that describe if they chilled or hot - soon a reality?

By the use of a printed temperature sensitive label on the package a consumer can quickly discover if the content is ready for consumption, or if it is time to put it into the fridge for further cooling.

The inclusion of temperature sensitive inks on a package opens up many possibilities for different smart applications. For example, at room temperature a soda bottle can have a very minimalist design, but when the bottle is chilled to the perfect drinking temperature, a nice coloured pattern appears.
Another application could be a small label on a milk carton that is solid blue when the package is inside the fridge or still chilled at the breakfast table. However, as the temperature is increased, at a certain point the milk starts to spoil. The smart label can be controlled so that the solid blue ink disappears and the text put back in to fridge appears at this temperature when it starts to spoil.

The inks behind this technology are called thermochromic inks and they are available in many different nuances and the temperature ranges that they operate in can be controlled depending on application. Thermochromic inks have actually existed for a long time, even as far back as the 70s, but they have never seen broad commercial use in paperboard packages. Why have not Tetra Pak or any
other big packaging material production company applied this technology?

There are two reasons for this. Number one, historically the high temperature that is present during lamination have damaged the thermochromic ink. This is as of now no longer a problem. By analysing the performance of various inks from the two contemporary ink suppliers CTI and LCR Hallcrest before and after lamination this conclusion could be drawn. The second reason is due to food safety.
This is because of the special chemicals included in thermochromic inks, often the infamous Bisphenol A, among other substances. The inclusion of these substances makes serious demands on safety related aspects of the manufacturing process of the prints. In addition, it is not yet clear if particles in the thermochromic inks diffuse through the packaging material into the content of the
package. Further studies have to be set up to answer these questions.

In summary, the inclusion of temperature sensitive labels on food packages could potentially create many interesting applications that helps the consumers. However, the consumers have to wait a bit longer as the food safety related aspects of the technology are evaluated.

• author: Bäckman, Martin
• supervisor: Niklas Andersson
• organization: Chemical Engineering (M.Sc.Eng.)
• course: KET920 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: chemical engineering, kemiteknik, thermochromic ink, termokromisk färg, colour changing ink
• language: English
• id: 8905340
• date added to LUP: 2017-04-19 11:02:43
• date last changed: 2017-08-01 09:58:58