Adhesive Applications The requirements of labelling
for the food industry Shoaib Akram from AA Labels says the breadth and scope for labelling is best illustrated when we turn our attention to the requirements of the food industry
A
s with all industries, the label is primarily used to communicate details on the content, such as legally binding information that must be shared, specifically for the food industry, dietary requirements, ingredient lists, allergy warnings, and sell-by dates. Losing this data from a label being lost due to poor adhesion or issues leading to the product spoiling is not an option. Therefore, we will focus on the importance of the correct label adhesion for the food and drink industry, looking at how this is used for heat resistant, freezer and cryogenic labels.
HEAT RESISTANT LABELS
When labels are subject to high temperatures, it calls for a more complex application structure which can also cope with heat increases. Heat resistant labels which are adhered onto hot steel after it is rolled are therefore created to withstand temperatures of up to 125°c. To ensure the longevity of food and drink labels, ensuring ongoing identification, traceability and safety, several different types of heat resistant labels have been developed: 1. Labels applied at ambient temperature and then heated up afterwards;
2. Labels that are applied when the product is already at a high temperature; and
3. For circumstances where the product is heated up and cooled down several times.
FREEZER LABELS
Labelling used for frozen items face as many challenges as those subject to high temperatures. Considerations include: • Whether the labels are designed to be adhered at ambient temperatures and then the adhesive is cured by the freezing temperatures after application. If these labels were applied to frozen goods, the adhesive would not cure and they would drop off easily; and
• In some cases, the goods will need to be frozen before the label is applied, therefore there are materials available that can be stuck directly onto frozen goods. However,
application to transient layers of ice should not be attempted.
The AA Labels range has a service temperature from -20°c to +80°c, with a minimum application temperature of 0°C. These labels are an uncoated paper material and have an acrylic emulsion adhesive designed to operate at low deep freeze temperatures.
If freezer labels are used at room temperature, the label only forms a semi-permanent bond. As the temperature decreases the bond becomes stronger and has a definite permanence.
CRYOGENIC LABELS
This type of label is made from a thermoplastic film and coated with a glove-friendly cryogenic adhesive. The labels remain strongly attached to a range of materials including stainless steel, aluminium, painted metal, powder coated metal, iron, borosilicate, Pyrex and other temperature resistant glass during a long-term storage and numerous freeze/thaw cycles.
They have efficacy inside a liquid phase liquid nitrogen, vapour phase liquid nitrogen, freezers (-120°C, -80°C, -40°C and -20°C), dry ice, freezer chamber, freezer room and other extreme cold environments.
Cryogenic labels can be used for identification of freezer racks, cassettes, X-ray film cassettes, film cans for archiving and other stainless steel and aluminium boxes, drawers, sleeves and canes for cryogenic straws, tools, equipment and metal objects inside freezers and all glassware in freezer rooms, liquid nitrogen tanks and liquid helium. They are available in roll and sheet formats as printed or plain labels and compatible with laser (sheets) and thermal transfer (rolls) printers, for over-printing.
QUALITY & TYPE OF MATERIALS In addition to matching the requirements of the label with adhesive type, the quality and type of materials used is an essential component. Whether the substrate you’re using is plastic, traditional paperboard, or a sustainable tree-free alternative, the composition is key to the success of the labelling.
For instance, plastic substrates such as polypropylene and polyethylene do not bond well with acrylic-based adhesives. As a result, this may not provide the robust nature of a rubber- based adhesive.
Material texture also factors into an adhesive label’s performance. If utilising pressure-sensitive adhesive labels, the substrate surface must be smooth enough to provide thorough contact with the label. This is because rough surfaces make it difficult for pressure-sensitive labels to adhere as the coarse texture reduces the amount of surface area meeting the adhesive.
Taking pebbled plastic or corrugated surfaces as an example, they are problematic for pressure- sensitive adhesive labels. So, if your preferred substrate consists of a rougher material, more aggressive adhesives can be implemented to offset the lack of surface contact.
We would advise not overlooking the impact packaging shape has on adhesive labels. When being applied, pressure-sensitive adhesive labels need a short period of time to move onto a substrate’s surface and properly adhere. If a rigid label is being placed on a curved surface for instance, the label may bend upwards before it has sufficient time to attach to the substrate surface.
PERFORMANCE FACTORS
Every label adhesive has three main performance factors:
Tack, or the label adhesive’s initial attraction to a surface with minimal pressure. An adhesive with strong tack will hold firmly to a surface with very little pressure, while an adhesive with weak tack may need consistent pressure over time for a strong seal;
Adhesion, or the strength of the bond between the surface and the adhesive after applying pressure to the adhesive. Low adhesion may remove with little to no residue while strong adhesion makes a label virtually impossible to remove without residue or damaging the label; and Shear, or the amount of strength it takes to pull a label across a horizontal surface in a direction parallel to that surface under specialised testing conditions.
14
March 2023
www.convertermag.com
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