Sandwich structure of packaging materials

In a previous post and in a video on SIPOS TV, we have already discussed what the different types of foil are, what their features are and how they can be recycled. In today’s blog post, we look at the sandwich structure of packaging materials.

What does sandwich structure mean in the packaging technology?

By sandwich structure we mean that the packaging material is made up of several layers. Just like a real sandwich: which can be made up of, say, bread, butter, salami, cheese and bread again. The wrappers can also be made up of an outer, an inner and even a middle layer, the most common sandwich structures being three and two layers. However, each layer has different features. Sipospack glues and laminates these different films together to create the sandwich structures of the packaging materials.

What can each type of foil do?

The most common sandwich structure for packaging materials is where the outer layer is a PP foil, the middle layer is a metallised PET foil and the inner layer is a PE foil. Polyethylene plastic has the property of melting well and being soft. The middle layer is a foil that has stronger gas, oxygen or even light barrier features. The outer layer is classically thin, but is also a visually eye-catching part of the packaging. Polyester is also common in these structures because it tolerates heat well, so when the packaging is sealed, welded together in an assembled multi-structure package, the outer layer does not melt, only on the inside.

From multiple materials or from one?

The disadvantage of these traditional triplex laminates is that they are made up of multiple materials, and these materials are difficult to separate and cannot be recycled later. That is why the packaging industry has already created special foils where these three different features can be achieved by using one type of base material, Sipospack is also working with these. We use these films for both single-layer and multi-layer packaging, with the product always determining what kind of packaging is required.

The advantages of single-layer packaging

If the packaging is single-ply, say 100% polypropylene, it is also completely recyclable, while having the features expected in the packaging industry, such as high gas impermeability or strong aroma barrier, chlorine-free, easy to print on, laminatable, pasteurisable. In appearance, this type can be transparent, white or metallized, that is, coated with metal. Easily recyclable sandwich structure packaging can also be made from multilayer polyethylene films. PE packaging is characterised by its light weight, good formability, high strength and also resistance to chemicals or moisture. In the food industry, we recommend it mainly for the packaging of dairy products, fruit juices, pastries and frozen goods.