How It Works: Irreversible Temperature Indicator Labels

How It Works: Irreversible Temperature Indicator Labels

Each temperature indicator label contains many component parts, all working together to give an accurate colour change when a specific temperature is reached.

The key components at the core of the label are a number of active layers – and remember we’re talking very, very thin layers. One of these layers is a carefully formulated white wax which is located over a layer of black paper. When heat is absorbed by the paper it expands – like a sponge – whilst melting the wax. The wax seeps through the black paper, giving the visual colour change from white to black. A red paper can be used to give a white to red colour change. Each reaction temperature needs a different wax, and these have been tried and tested over many years to ensure reliability and consistency. One advantage of this is that we have a wide range of temperatures available across a wide range of different labels.

This whole process of the colour change takes a maximum of about 4 seconds, with that time decreasing if an indicator temperature is exceeded very quickly. All the labels are backed with adhesive and a good seal to the surface is part of ensuring the indicator works well. It also makes the labels oil, water and steam resistant.

The colour change is irreversible; once the change happens, it is permanent. We recommend users position the indicator label in situ, then observe, note the reaction and then remove the label when the observation is complete. For some users, that can test process be a matter of minutes or even seconds, for others it can be months if the label is being used for longer term observation. Removal tends to separate some of the layers, affecting the visibility of the colour change. As a result the labels tend not to hold up too well to being removed and stored as permanent records. Customers that need a permanent record should contact us to discuss the options, such as cost-effective printing solutions where we print a card onto which the indicator is placed, allowing data to be recorded alongside the temperature indicator label. One such example of this kind of bespoke product design was a foil backed card that we printed on the paper side with various boxes and data to allow information to be recorded alongside the temperature. The temperature sensitive label was then positioned in a prominent location to allow food plant operatives to easily check if the required cook temperatures had been achieved. The indicator and card combination was for use in a food processing plant and was to accompany a cooked meat product on a production line. The manufacturer didn’t like the idea of the card potentially being damaged and consequently retained in the product as a contaminant, so we decided that a foil card would be a good way to rapidly determine any problems. All the cooked meat went through a metal detector at the end of the process and any fragments of card that had come away in the process would be detected and could be easily removed. The cards worked very well and were retained and stored for validation of quality assurance / control procedures.

The temperature indicating labels react according to the temperature of the surface to which they are applied – that is they react to what they are stuck to, rather than atmospheric / external conditions. It is important to ensure they are placed on a clean, dry surface and we often recommend users to paint a layer of clear epoxy over a label if it is going to be exposed to aggressive conditions.

Storing the indicators in a refrigerator before use ensures a good shelf life and maintains accuracy – it keeps the wax from drying out, which inevitably happens over time. The indicators typically have a one year shelf life, with a two year shelf life for some higher temperatures.

One thing we’ve learnt over time is that every application for temperature labels is unique. We pride ourselves on our ability to advise our customers on the best way to use our label products but also on their limitations. We keep our prices very competitive, our minimum order quantities are very small and we offer bulk discounts for large volume orders. 99% of our items are in stock and can ship within 24 hours. Email us with any questions – we’re here to help.

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  • Tim Arrowsmith