Caviar is highly valuable and sensitive, and its packaging is a very decisive factor in the quality of the luxury product. A long-established technique applied to PET bottles is now finding its way into the foodstuffs industry: the multi-layer container with barrier. It offers foodstuffs producers a cost-effective, flexible and safe alternative to the conventional tin.

No question, a delicacy such as caviar must be packed properly. At present this means that the black pearls are normally packed into tins, which are coated on the inside and regarded as ideal for fresh caviar. The only real alternative so far have been glass jars of different sizes.

Alternative packaging.
A new alternative is now available: multi-layer packaging based on the co-injection technique. The concept was developed twenty years ago for the beverages trade and has proved its worth ever since in an increasing number of areas. Fruit juices, such as orange juice based on concentrate, sensitive dairy products and beer or wine benefit from this technique when it comes to shelf life and quality. Thanks to this innovation, the shelf life of, for example, beer is lengthened to up to six months. Without this barrier, the refreshing drink would be flat and tasteless after only one week.

Improved shelf life.
Otto Hofstetter AG has contributed decisively to the development of the multi-layer concept with co-injection. The company is now permanently engaged in bringing the technique to perfection. In cooperation with MIR Upakovki, a well-known Russian producer of packaging articles, the process has been adapted for the packaging industry. The production of barrier tubs for caviar has been running since summer 2011 and has been certified by the Russian Federal Research Institute of Fisheries and Oceanography VNIRO. The tested multi-layer container for salmon and caviar provides microbiological safety for twelve months at storage temperatures from – 6 to – 4 degrees Celsius and eight months at 0 to + 5 degrees Celsius.

Barrier protection.
The built-in barrier layer of EVOH copolymer is the key aspect of this technique. The properties of this material act as a gas barrier which keeps oxygen away while retaining the flavour and quality of the foodstuffs. Even in the case of sterilized or treated products, such as baby food, the barrier effectively protects the vitamin content.

The co-injection technique
offers maximum precision for the oxygen barrier.

The co-injection technique is a further advantage of the new development of Otto Hofstetter AG and MIR Upakovki. The precise process cannot be matched by conventional vacuum forming.

Efficient production.
The precision is due to the co-injection technique, which en-ables the packaging container to be made in one operation based on a two-stage process. In a first step, the container’s outer and inner layer are injected through two channels, whereby the nozzle pin is fully opened. In the second step, the barrier material, e.g. EVOH, is injected into the mould in parallel, but with a time delay. The exact distribution and height of the barrier material is achieved thanks to a highly precise hotrunner system.

Maximum effect.
The quantity of barrier material depends on various factors, but the aim is to keep the layer as thin as possible. At this time the wall section is less than one tenth of a milli-metre. However, the barrier thickness can vary depending on the
packaging article. The decisive factors are the product geometry, wall thickness, flow length and viscosity of the plastic materials. In the choice of the barrier material, it is important that the processing temperature is similar to that required by the other material component. There are virtually no limits as regards colour. The only aspect to be watched is that the colourant carrier is compatible with the basic plastic material.

Parameters for success.
If you intend to produce multi-layer packaging using the co-injection technique, you must consider some important aspects in the development. The maximum protective effect is achieved only if the barrier layer covers the entire moulding surface without gaps. Even a small opening in the layer will increase the gas permeability with the result that the effect may drop to nearly zero.

Simple shapes froma flow-technical point of view are the most suitable for the production of moulded articles with a barrier layer. In other words, shapes which allow the barrier layer to spread easily over the complete surface. If the packaging container features a U-shaped rim, the protective layer can be drawn right up to the lid-sealing area. Shapes that cause an interruption of the advancing flow front are less suitable.

The future has started.
Compared with tins and jars, polymer packaging products with a barrier layer are impressive in many respects. For the same capacity (product content) they are twenty times lighter than a glass jar and three times lighter than a tin. They are stackable – an important factor in both storage and transport. Another plus is the fact that fewer containers holding valuable foodstuffs are damaged or destroyed on delivery. In addition, it is possible to install an in-mould labelling (IML) system to increase the processing efficiency and enhance the design possibilities. Using transparent or coloured raw material enables further design variants to attract more attention on the shelf.

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