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Expert Article

Paul Whelan, technical manager at Chadwicks, guides you ?through the complex world of pre-cut lids

Lids can seem such simple things – a cover that protects the contents of a food product. However when it comes to selecting the appropriate materials for lids, the subject can become a bit of a minefield.
 
To make the manufacturing process easier and quicker, experts here at Chadwicks are best placed to advise food and non-food manufacturers on which materials would best suit their product to ensure the creation of a durable, user-friendly packaging solution.
 
Heat seal pre-cut lids are compatible for use with a range of packaging applications including containers for cream, yoghurt and ice cream, beverages, snacks, butter and margarine, as well as other non-food items. Certain products however require different qualities in a lid, in addition to design variations to give it that edge, and here you can find out about the different materials and options available.
 
Polyester lids
 
Polyester is a standard product, available in gauge .050 with pin dot embossing and can be used for sealing to PS, PP, PET and Paper PE container types. The advantages of using polyester as a lid material include its availability as a white surface, which provides improved graphic quality and colour definition. As a transparent touch-clear polyester and also with a partial heat seal lacquer, it becomes one of the most versatile materials available on the market. What’s more, polyester is a non-metallic material that allows for ‘end of line’ metal detection, vital in food production and testing. Metallised polyester (MET-PET) gives the lid a metallic surface and improved barrier properties.
 
This widely used material provides high puncture and tear resistance, which is important for storage. It can also be micro-perforated for easy separation of multi-pack lidding, making products very user-friendly.
 
Aluminium
 
Aluminium based lidding is another standard product for sealing to all container types such as PS, PP, PE, and PET. Aluminium can provide the important advantage of providing a total barrier against water vapour and oxygen transmission, as well as light and aroma. This therefore makes it an ideal choice for sensitive and extended shelf life products.
 
Available in gauges .029 / .037 / .048 / .060, its metallic properties can be used as an aesthetic feature of the lid design and logos can also be embossed, as well as featuring standard patterns such as random grub and fine linen.
 
Aluminium with heat seal lacquer is primarily used for short shelf life products such as yoghurt, yellow fats, cream, etc. Special lacquers are also available for more “aggressive” products such as cheese. Aluminium with a co-ex sealing layer is another option which - because extrusion coated materials do not use solvents in the heat seal layer - can be considered more environmentally friendly than heat seal lacquered material.
?The thin plastic sealing layer also offers ‘easy’ low temperature sealing and increased protection for aggressive products. Certain specifications are also suitable for hot fill and retort applications. Surlyn (heat seal to glass co-ex) can also be used for sealing to both glass and tin, whilst recess diaphragms can be manufactured using laminates, lacquer and co-ex materials. Other advantages include the elimination of container warping or panelling when packing hot-fill products.
 
Laminates
 
Laminates are another adaptable material primarily used for “aggressive”, corrosive products or those that require additional processes such as cooking or hot fill.??Laminates can offer a weld (un-peelable) seal, which is ideal for chemical-type products, while certain laminates offer easy peel functions and are used for food packaging where the consumer requires a good peel with a reduced risk of tearing the lid.
 
Available in gauges .040 / .048 / .070 and with HDPE, PET and modified PE as well as in combinations such as .012 and as PET/.048 aluminium with heat seal lacquer, these properties can provide increased tear resistance for high value products such as ‘ready to drink wine goblets’.
 
Also offering total barrier protection from water vapour, oxygen transmission, aroma and light, laminates are an ideal choice for sensitive or extended shelf-life products. Another feature includes logo embossing, in addition to the standard patterns such as fine linen and random grub, or alternatively customers can opt for no embossing at all.
 
Finally, a non-aluminium laminate is also available using .065 Polyester with an .040 cookable and peelable PP sealing layer for products such as p

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