Flexible Packaging
Retort – an energy cost saver By Tom Kerchiss – RK Print Coat Instruments.
A
t a time when energy costs in much of the world is set to skyrocket, hard-pressed consumers are looking at ways in which energy costs can be eased, though not solved. Could retortable systems, a flexible packaging medium that first saw the light of day in the 1960s work out to be energy and cash cost saver in these troubled times? As with many processes and products that we as consumers take for granted today, the initial resources to bring a product to fruition were initiated by the military either during or just after a war – and this is certainly true for retort packaging. When the US Army began to look for a replacement for the bulky and unpopular C-Rations (canned) field and command rations in the late 1950s early 1960s, the project given the acronym MRE or Meal Ready to Eat engaged the attention of food scientists and packaging technologists and directly resulted in a retort system that was suitable for its military purposes, but not really suitable for the consumer market. It was a case of waiting for the market to catch up and for consumers and food product producers and packaging technologists to consider whether retort packaging or pouches was relevant.
Advances in technology such as more compact and affordable microwave ovens as well as susceptor technology have extended application possibilities and made retort packaging more acceptable as a packaging medium in some markets, notably Japan but also other countries in the Far East. These susceptors integrated within a pack, and which take the form of patches absorbs and alters (active packaging) the microwaves so that food packed in materials that repeal microwaves such as foil can be heated or cooked via conduction or by infrared. The materials from which retort pouches are generally made from are either aluminium foil used in conjunction with plastic laminates or alternatively foil-free laminates. The construct itself must be inert, heat sealable, dimensionally stable and heat resistant. During processing the food, which may be raw or part cooked is sealed within the retort pouch and sterilized at temperatures of up to 1210 centigrade for several minutes under high pressure inside an autoclave or retort machine.
Low oxygen and water vapour permeability is essential and the retort pouch must possess good aging properties. Constructs without aluminium foil are transparent. Polyester as an external layer gives the structure strength, provides for strength, an inner ply of polypropylene is used for its heat-sealing capability, strength and for its compatibility with many food
items. Laminates of other materials can be used, polyamide for example improves durability and is frequently used on products destined to be sold in Japan where pouched products may be sold singly and not packed and stacked in multi-pack cartons, which is frequently the way retorted goods are sold in European and North American supermarkets. Metalized coatings of silicon oxide, Si0x and aluminium oxide AI0x provides for additional barrier resistance and improve microwaveable properties. Layers are laminated together using specially developed thermo stable adhesives. Retortables are reverse printed on a PET film prior to lamination of the various layers to avoid migration of inks and components. Gravure is for the most part the print process of choice.
Retort pouches are available in a wide range of configurations and sizes from single serve pouches of vegetable juices to catering pack sizes (10 servings) of soup. Stews, curries, fish in sauce, dried and sliced fruits are just some of the items that are retort packed. Retortable systems are space saving and in many instances serve as a good replacement for canned products. Recent research undertaken in the United States indicates that changing demographics, single person house occupiers, less living space and in many instances the only cooking appliance that the home owner has access too is a microwave could be a driver of growth for retort pouched products. In the UK 11% of city new builds for single occupancy do not have space for a conventional cooker to be installed. Where as more than a billion retort units are sold annually in Japan, the European, UK and North American markets for retort items has up until now been disappointing. Energy savings, the fact that microwaveable meals can be cooked in seconds, minutes at the most, saving on food wait times and on gas and electricity may help to drive up the sales of new products currently being developed. Furthermore many of the items that are suitable for being packed include the fastest product shifters, the vegetarian and vegan foods. Retortable products can help with calorie-controlled diets and the format is ideal for the packing of gourmet food items. Research and development is on going into new laminating material, the testing and trialling of adhesives and formulations. Quality control, presentation and appearance are as ever high on the agenda.
Colour, graphics, the development of inks, coatings and adhesives matters and can’t be left to chance, trials, prototyping determining commercial and product viability can be undertaken using systems
such as RK Print Coat Instruments VCML Lab/Pilot Coater or bespoke pilot/production VCM Coater. Lamination allows for an almost limitless range of materials and structures to be combined. Lamination, both wet and dry bond can be undertaken on the VCML Lab/Pilot Coater and the system, which has a working web width of up to 300 mm offers hot air, infrared and UV curing options.
The VCML Lab/Pilot Coater enables users to print, coat and laminate on all types of flexible substrates. Various coatings including inks, varnishes, adhesives and even paint made up of water based or even solvent materials can be applied. The system, which is configurable and offers a wide range of selectable coat head and print technologies, allows for short run production.
Being able to explore and exploit different process methods can result in production cost savings and in improved production. For example, different coating technologies can be set up and products run to determine which of the many coating options provides for the most uniform coating deposition of an ultra thin coating on an ultra thin substrate. Trialling off production machine facilitates exploration, minimises on production machine waste and can be an invaluable aide in improving workflow practices and by association competitiveness. As mentioned the VCML Lab/Pilot Coater can undertake wet and dry bond laminating. Dry lamination differs from wet lamination in that the liquid adhesive is dried prior to lamination. The adhesive can be applied to one layer and dried; alternatively the adhesive can be applied as a hot melt filmic layer so that the adhesive in effect becomes another layer of the laminate.
Bonding is generally achieved at high temperature and high nip pressure is sufficient to cause adhesive flow. As it cools and gels an effective bond is created. Unlike wet bond laminating the dry bond method can be used on a wider range of substrates including film and film with foil.
www.rkprint.com
24
March 2022
www.convertermag.com
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