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Converting Case Study


A barrier when packaging By RK Print Coat Instruments Ltd’s Tom Kerchiss


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ackaging material selection and the matching of inks, adhesives and coatings is more often than not job specific and it is often one of compromise. To some extent, it’s a case of selecting materials and consumables that are the most suitable for the product that is to be contained, protected and displayed. These may not, necessarily, be the cheapest or what that the designer and others with a say in how the product is presented and displayed may have preferred. The limitation, lack of a particular machine or process, and/ or lack of experience in-house, at the printer or packaging converter may also influence process and material decisions, as will permeability; the degree of barrier resistance that the product demands.


Food doesn’t stay fresh forever. Many foods deteriorate when exposed to oxygen. For example, fats can be oxidised, resulting in tainted food. Bread goes mouldy and red meat turns brown and develops an off-smell. Packaging technologists tread carefully to ensure that the permeability or barrier- resistant properties of the packaging material or polymer materials is appropriate, without wasting costly material.


Light can trigger oxidative reactions, so certain foods need a barrier in place to prevent light-induced changes that affect nutritional value and produce off-flavours. The moisture content of many foods needs to be monitored and controlled. For example, wheat products, like flour and pasta, are hygroscopic, so the moisture content is affected by humidity and temperature. For food items, such as leavened bread, tortillas, Panettone and fruitcakes, humidity or the lack of moisture can be problematic. Too dry an environment will shorten shelf life and impact on quality. For example, pasta can become brittle and crumble. However, it is also prone to discolour if there is too much moisture or humidity. Pasta, rice and multi-grain foods are often packed in flexible packaging. High-quality leak-free seals or welds are critical for flexible packaged items. If the product has been subjected to modified atmosphere packaging or an aseptic process any failure of the seal or weld paves the way for microbial contamination.


Improvements in polymer film technology, coupled with inorganic and organic surface treatments and coatings, make it far easier to source material that meets various objectives, such as a specific heat-seal threshold, gloss, clarity, flexibility without cracking and product resistance.


As I mentioned earlier, material selection can be a trade-off. Some polymeric films have an intrinsic barrier to moisture or oxygen, but rarely both. It is essential that the physiological processes of the food product are understood, notably the metabolic processes associated with respiration and transpiration. For packaging certain foods, the composition; the fat content, pH and aroma compounds can impact the sorption characteristics of some of the polymers. Environmental factors, such as temperature and relative humidity, can compromise permeability and barrier resistance.


MAP PACKAGING


Vacuum and modified atmosphere packaging ranks highly when it comes to considering process options for foods, such as filled pasta, rice, caryopsis cereals, flour and many bakery goods. Modified atmosphere packaging or MAP can be a passive or an active process, whereby the internal compartmentalised atmosphere of a pack is regulated in order to slow down microbial and enzymatic deterioration. The difference between active and passive is that, with the former, gas flushing is involved. Typically, nitrogen and carbon dioxide are used to remove/regulate oxygen from within the pack at either the manufacturing stage or at distribution. Gas scavengers or absorbers are used to establish the right mix and to maintain equilibrium. The materials associated with modified atmosphere include mono-layered side weld bags; multi-layer, co-extruded materials and custom configured laminated assemblies. Laminated pouches and other flexible products enable the formulator, manufacturer and converter to enhance or overcome barrier and processing problems. For instance, the effectiveness of a material such as EVOH, which offers excellent gaseous barrier properties, can be compromised if it


absorbs too much moisture; the solution is to sandwich it between two layers of a moisture resistant material such as polyethylene. Lamination allows for an almost unlimited range of structures to be combined together, providing that the overall thickness is no more than 400 to 500 microns. Once the plies are combined, they provide cost benefits and exceptional barrier-related properties, when compared with processes such as co- extrusion. Lamination is the only process that allows for aluminium foil, paper and other non-plastics to be used in combination. For many items that are for display and sale in a retail environment with fast product turnarounds, vacuum packaging is easier to process and is less costly than MAP. Vacuum packaging can extend the refrigerated life of a perishable item; in some instance three- to-four times the normal refrigerated life. In practice, moist air surrounding the food item is removed and the pouch is sealed. As oxygen levels fall, carbon dioxide increases, which slows the deterioration of the food.


SPOTTING POTENTIAL PROBLEMS Regardless of material and process selection, product appearance and performance need to be monitored; different materials and formulae have to be evaluated so that best-available materials, inks, coatings and coating technologies are chosen. It’s important that substrates/inks/coatings and various laminates under consideration are compatible. In some instances, it’s essential that converters and supply chain providers approach tasks with an open mind, so as to weigh up different processing options. One method of coating may be economically more advantageous than another, or a certain material, when used in conjunction with a particular coated adhesive, may increase the possibility of de-lamination at some point. Products need to be trialled under real-world processing conditions, potential problems highlighted, so they can be resolved prior to commercial production.


u rkprint.com convertermag.com December/January 2021 47


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