June 30, 2016 Uncategorized No Comments

S
ingle layer packs have for many years formed the bulk of food packaging, be it for bags, film or rigid containers. The reasons for this have been ease (cost) of manufacture and low cost to users (manufacturers). The disadvantages of single layer packs, are carried by both manufacturers (packers) and end users (consumers). Packers have to retract unsold stock that has passed sell by dates, this stock is then destroyed or re-processed, and the container also has to be recycled to prevent environmental harm. Consumers of course are faced with products that go off before they’re used, a waste of money and an inconvenience as well. Again the environmental impact of disposing of the products has to be considered.

MULTI-LAYER

Multi-layer packs, whether co-extruded or laminated offer multiple advantages both to manufacturers (packers) and consumers. The disadvantages of single layer packs can be overcome by adding layers that shield from UV light, prevent oxygen ingression or otherwise protect the product, maintain freshness and extending shelf life and reducing expensive transport requirements by better protecting the product.

FLEXIBLE PACKAGING
Flexible packaging utilizing multi-layer technology can be seen everywhere, from banana packaging, to tea (light sensitive) to wine in flexible bags (oxygen ingression) to tough blister packs that almost defy human attempts to open them. What is the most interesting with many of these packs, is that the consumers who buy them and use the contents, have for the most part, no idea of the technology keeping their food fresh and protected.

RIGID PACKAGING
Rigid packaging is similar, but with some noteworthy differences. The process used to mould rigid packaging was for a long time restricted to single layer due to technical limitations on extruders. The materials used also imposed some limitations; some materials do not lend themselves to multi-layer processes. PET is one of the more difficult materials to process in this manner, its monomer composition making it difficult to inject a second layer at the preform stage. Other methods tried have included 2 part injection of preforms, but this results in secondary processing difficulties when blowing. The capital investment in a co-injected PET plant is significant and each system has to be designed around the container. The co-injected materials have to be carefully selected due to the monomer properties of PET that are susceptible to delamination. Recycling of co-injected preforms is limited to less critical applications downstream. Application of co-injected PET in dairies while attractive, does not address all of the barrier properties needed to maintain product integrity for longer periods, while significantly raising the cost of the packaging.

Currently, for rigid packaging in multi-layer (up to 6 layers) the best option is Extrusion Blow moulding. The reasons for this are varied, but they’re extremely compelling.

  1. Ease of processing – The multilayer technology is built into the machine, not the moulds.
  2. Flexibility of mould shapes – because an extruded parison is used to blow containers different shapes are easily achieved, including punched handleware. This is not possible in a process that uses injection as its primary process.
  3. Colour and layer versatility – The multi-layer process lends itself to colour changes as well as layer (properties) changes. This offers the manufacturer and end user a highly versatile way to manufacture property specific containers. It would be possible to use a 6 layer system on 3 layers only, simply by changing the materials in the respective extruders, because of the nature of extrusion, there would be no impediment to that.
  4. In line recycling – The nature of the process allows for inline recycling of tops, tails and in the case of handle ware, punchings at the machine, where the off trims are immediately recovered before they can become contaminated, granulated and fed into the middle layers of the extrusion process resulting in no offsite reclamation of material. It also results in a zero loss position on material utilization allowing for more competitive quoting on containers by manufacturers.
  5. Dairy Applications – In a dairy environment, multi-layer technology can boost profits by reducing spoilage and creating a buffer to cold chain irregularities. In a South African context, this can add up to substantial profits, due to many retailers and producers outsourcing cold transport, a process which they have no control over, but in many cases have to carry the responsibility for.  Extrusion also offers the aesthetic attractiveness of traditional shape packs with the advantages of multilayer technology, without resorting to squared off user unfriendly no-handle packs
Written by Toni Goncalves