The lightweighting of plastic packaging is still on the rise, as many producers look to remove excess material from their containers to meet e-commerce, material waste reduction and other pressures. However, lightweighting has an unwanted side effect in some plastic packaging. Here John Grover, Director of Sales, Americas at Selig Group, a global leader in container sealing and venting technology, discusses the problem of distortion and how it can be resolved.
Whether through geometry optimisation or thinner walls, plastic lightweighting can deliver lower material costs, a reduced carbon footprint and improved transport efficiencies. A great case in point are HDPE plastic milk bottles which, in the UK, have reduced in weight by 23.8% and their caps by 41.6% over the past 13 years.[i] However, when wall thickness is decreased by even small amounts, unexpected container deformation can occur.
A range of packaging design solutions are used to overcome this including the addition of ribbing, curved panels or grip zones, using a modifier to strengthen the base material etc. Another solution is to utilise the stabilising properties of vented foam or induction heat seal liners, as they allow lightweighted plastic containers to retain their intended shape by equilibrating internal and external changes in pressure.
Household chemical and concentrate lightweighting challenges
Containers that can pose a particular lightweighting challenge are those that contain products prone to off-gassing or oxygen scavenging - such as home and garden chemicals – or more ‘concentrated’ forms of these products. The two main distortion issues seen are panelling (when the walls of a plastic container collapse inwards) and bloating (when they swell or bulge outwards). The former tends to happen as vacuum pressure is created due to product oxygen scavenging, or elevation or atmospheric pressure changes. Bloating on the other hand is a result of gas buildup inside the packaging, such as in the case of concentrated bleaches, peroxides, and other household cleaners and chemicals. Alternatively, if the product absorbs gas - which tends to occur with solvent-based products and those containing essential oils, then there can be panelling.
Venting to maintain appearance
Although panelling and bloating do not tend to have an impact on the container’s contents, they can communicate to consumers that product spoilage might have occurred, reducing their shelf-appeal. To avoid these issues, whilst continuing to meet lightweighting plastic reduction goals, the answer lies in ensuring proper venting.
Venting is the use of a sealing liner that has been designed to allow pressure equalisation through letting gas in or out. Microporous membranes, slit or pressure-relief valves and two-piece vented liners can all resolve the panelling and bloating issue. However, it is important to choose the right vent, as some only work if the container is stored upright, and the incorrect vent liner choice can leak if the membrane is compromised.
When it comes to containers for items prone to bloating and panelling, it is advisable to use closure liners that include a hydrophobic or oleophobic membrane. These membranes allow gas to pass through but block liquid escape, maintaining a secure, leak-free seal, even under pressure. A good example of these membranes are Selig’s Circumvent™ and AirFoil™ family of products, that are helping many producers lightweight their containers, whilst eradicating potential panelling or bloating issues. Other venting solutions for use on specialised containers or in custom closure systems are also available from Selig.
As the balancing act continues between meeting e-commerce, material waste reduction, cost saving and regulatory targets and maintaining the container’s on-shelf appeal, vented liners are an unsung hero in the packaging producer’s toolbox. By choosing the right container venting solution, it is possible to deliver both plastic reduction and container integrity in even the more challenging applications.
[i] HDPE plastic bottles for milk - in1992, containers weighed 34.04g. Over the next ten years this was dropped to 25.95g; a 23.8% reduction in weight. In addition, the PE cap on the bottle was dropped from 3.1g to 1.5g, a 41.6% saving in material. These great gains were achieved using an induction heat seal, to give the lightweighted containers both stability and tamper evident product security.
For more information on Selig’s global capabilities and solutions, visit www.seliggroup.com,