Do materials for steel-based packaging belong to the past or the future?
When dealing with this Web frequently, the most common problems that arise in the use of cans, can lead to think that they are already inadequate means. On the contrary, having been advised on their limits and possible incidents, it is much easier to use them within a sufficient margin of safety and take full advantage of their advantages. We dedicate the following comments to the main qualities of steel-based packaging. The problems presented by corrosion, which occur in a very limited number of cases, are a minority compared to the positive aspects of tin containers.
In the past, the production, transformation and use of tinplate were the subject of numerous investigations, which have continued to mobilize today important laboratories belonging to three main links in the chain, specifically: the manufacturers of the material, the manufacturers of packaging and users. Currently, the most sophisticated laboratory equipment is used to improve the characteristics and performance of the material. The mass production of metal packaging at very high speed has been possible mainly by industrial engineering.
In the last decades of the last century, thanks to these research and development efforts, a series of new manufacturing techniques appeared: DWI (sausages, stretched and pressed), DRD (sausages and re-packaged), without omitting the packaging electrically welded, which replaced the side seam containers with traditional closure and soldiers with a tin / lead alloy. Also the systems of Easy Opening, that now are used of generalized form for the normal containers. It is accepted as an established fact, that thanks to the design and development of specific organic coatings (varnishes), the chemical inertness of the container is guaranteed.
If the production of metal containers has now reached such high precision and regularity, that it is at the limit of perfection, it is mainly due to the progress in the manufacture of steel, including cold rolling to the final thickness (reduced double tinplate). ), thermal and surface treatments, etc. So we have entered a generation of ultralight containers, with thin walls, which only a few decades ago was unthinkable.
This climate of research and innovation promotes partnerships and mutual assistance between the manufacturers of materials and the manufacturers of packaging on the one hand, and between the manufacturers of packaging and fillers on the other.
What are the technical advantages of steel-based packaging?
We will mention the most important ones without organizing them in order of importance, because they all interact with the 5 main functions that any food container should mainly satisfy:
– adequate content and conservation
– which constitutes a unit of food for consumption
– that can be easily produced and transported
– that is of practical use
– containing a message
Compared with these functions, the metal container has the following advantages:
– consistency and shock resistance
– integral isolation to gases and microorganisms
– absolute impermeability
– does not deteriorate due to heat or cold
– a good conductivity of heat and cold
– Magnetic material, therefore easy to handle and separate for recycling purposes
– Chemical inertia perfectly controlled due to the use of organic coatings
– an excellent base for decorative inks and lacquers
– easy recycling, ie ecological material
Briefly we will discuss each one of these:
a) The metal container is solid, with good impact resistance
It is unbreakable. Glass, its main competitor in some areas of food packaging is speculating about “becoming as resistant as steel”. When compared to other containers, the metal ones are not fragile during handling and transport and can deal with the mistreatment more easily. High elastic limits are inherent to steel.
b) The metal container is impervious to light, gases and microorganisms
This is an important advantage. It is necessary to preserve the biochemical and microbiological stability of the food. The damaging influence of light and UV radiation is a reality, leading to some modifications particularly of color and flavor. The metal wall of the container also constitutes a barrier impervious to all gases. The oxygen of the air, an oxidation agent par excellence, can not reach the food. Said impermeability to gases is also effective in the opposite direction. The gases that form inside the container, due to corrosion or microbiological alteration (insufficient sterilization or recontamination) are kept inside it, becoming deformed, thus showing abnormalities that are incompatible with the hygienic and sanitary nature of the product.
The metal container, which preserves the food processed thermally, is an effective safety against microbes for months, and even years. In particular, it protects the conserve against the pathogenic microbes of the environment. It offers a first-rate security to the possibility of almost duplicating microbes every twenty minutes at certain temperatures.
c) The impermeability of 3-piece containers is ensured by an electrically welded side seam and by the double closing of the ends. Embossed containers become waterproof only by means of double closing of the upper end. Unlike glass containers, which have to go to another material (in this case the metal) to achieve waterproofing, the metal container is a homogeneous system that will withstand differences in pressure with the outside of several bars. In a full container, which is maintained without the presence of internal corrosion, or of microbiological alteration phenomena, the internal vacuum is always maintained. In the same way, there is no loss of gas in carbonated beverages, during storage under any external climatic conditions.
d) The metal container is not affected by heat or cold.
Its physical, mechanical and chemical properties will withstand all temperature deviations observed in its environment, even occasionally high.
e) The metal container allows the transfer of heat and cold
The evolution in packaging technology is such that it allows more and more the cycles of “short and high” thermal processes (short time – high temperature). Steel is the most suitable for this evolution, which has improved the conservation of the nutritional and organoleptic properties of packaged foods.
f) The magnetic property of steel during handling operations is highly appreciated. Among all the packaging materials, it is the only one that benefits from this property. It makes their separation and selection in garbage before incineration or other disposal system very easy.
9) The surface treatment of tinplate and tin-free steel (TFS), allows the application of the best organic resins in very thin layers, with a high adherence, ensuring the chemical inertia of the metal. Thanks to these organic layers, the metal container, although it can not achieve the same inertia as glass, has been able to be applied to the preservation of an impressive number of foods and industrial products.
h) In the field of decoration, it is difficult to improve the presentation of tinplate, where tin, due to its reflecting force, highlights the brightness of the inks. Tinplate is the ideal choice for the manufacture of luxuriously decorated trays and boxes. Famous paintings have been reproduced in this material with great realism and quality.
In this field, it is worth noting that lithography of sausage packaging can be printed on a plane. For this purpose, a previous deformation (anamorphosis procedure) is used so that the decoration is provided after the training operation. This achievement is due to the combined dexterity of the metallurgist – who has become expert in the elongations oriented with reference to the direction of the laminate – to the ink and to the designer and manufacturer of lacquer, to the photomechanical specialist, to the printer and finally to the manufacturer of the containers.
i) Finally, the steel in the metal container is a material that does not harm the environment.
Nowadays, all materials used in the packaging industry are obliged to take an environmental factor into account. Of all the metallic materials, steel shows the most natural tendency to return to its original state, that is, to undergo an oxidation process transforming itself into iron oxide. It is, in its way, biodegradable over time. Its magnetism allows industrial recycling by means of the traditional domestic waste selection circuit, not like other materials (aluminum, plastics) that need more complex procedures.
The steel used for packaging materials is of extra soft grade without particular components. Its different characteristics, such as its elasticity, elastic limit, breaking load, etc., are essentially linked to the thermal treatments applied. The containers, once empty, can return to the steel industry in the form of scrap metal and will be converted back into steel. In this way the containers contribute to an energy saving.
The billions of steel containers currently manufactured each year in the world, are sufficient evidence that the material meets the needs of users. Metal containers with a steel base have the advantage of a good quality / price ratio.
Tinplate has not yet exhausted the possibilities of innovation. The engineers who work in the steelworks and in the steel mills continue to provide the container manufacturer with increasingly specific quality grades according to the way the metal works (expansion, stretching, etc.). It can be said that tinplate is a product that can be selected based on its use.
In the field of packaging, always changing, exclusivity is out of place and it is good to think that in the future more and more complex material will be used. In these future partnerships, the use of steel will not be in excessive danger.